We wish to make this key available to one and all in the hope of correct identification of minerals in collections, rock gardens, and on windowsills everywhere. You may copy it, or any part of it, for non-commercial, personal use.
We thank Lloyd Brown, David Jacobson, and Alfred Ostrander. Their excellent advice and encouragement in this project was extremely helpful. © 2000, Alan Plante & Donald Peck
Introduction
This Mineral Key is designed and intended for use on-line. It is intended also to be used in conjunction with one or more other field guides to minerals: Once the Key leads the user to one or more "likely suspects" details on them should be looked up in another book in order to make a final determination.The premise behind this Key is similar to that of the identification keys found in some fern and wildflower books: An artificial key is used to direct the user to the pages in the sections where further information on "likely suspects" are found. The information in the sections on mineral species is then used to narrow the choices to one or a few "most likely" species. Then more detailed information can be found in a mineral guide to make a final determination.
Unlike most keys for wildflowers, this system for the identification of minerals is limited – both in scope and applicability. Only a couple hundred of the most common or "usually seen" mineral species are covered. Users may well come across rare species which are not covered here. The system also requires good enough samples of the minerals to perform the tests in the sections describing mineral species. It is probably not useful for the identification of micro-crystal samples. Still, it can help narrow down the search by eliminating the more common species as possibilities. If a sample of some unknown mineral does not "key out" to one of the common species, then further testing and research to determine its identity might be worth while. But the user is cautioned that every possible effort should be made to key the sample out using this Key before looking elsewhere for help: Many common minerals have varied habits and other characteristics which might lead one to suspect a sample to be something rare, when in fact it is a common species in one of its less-prevalent forms. A close read of guide book information may clue the user in on such samples. Resorting to such things as sending samples in to a lab should be the last thing one does with an unknown. You should be quite certain that it is a rare species, one not covered here or in a mineral guide .
Often a single series of field tests may not key the user in to the correct identification. The odds of making a correct identification will be increased if tests are repeated: Take several streaks, especially if a sample is proving difficult to get a streak from), test the hardness more than once – and do tests both ways, trying to scratch the known hardness tool with the mineral and trying to scratch the mineral with the tool. If possible, when examining samples for cleavage, look at several samples – and try to use fresh breaks, cleavages which you – not nature – have produced. It is often a good idea to examine small cleavage surfaces using a 10X lens. If the first try at determining a hardness is unsuccessful or ambiguous, perhaps the second, third, or fourth will do the trick. The same holds for other tests. Such diligence to repetitive procedure usually pays off where a single try does not.
Finally, if the first run through the tests doesn’t seem to be leading you to the correct identification – try again from scratch. A second run through the entire procedure may do the trick – maybe rethinking some aspect of the tests, such as whether or not the sample really has a metallic luster. In the end, care should lead one to the correct identification for species covered in this Key. Also, practice may not always make perfect – but in the case of mineral identification the more you practice the better you will get at it. So try running samples of known species through the procedure to get a feel for how the key leads one step-by-step towards and identification. Practice, practice, practice…
[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]
A Simple Identification Kit
In order to use this identification key you will need to assemble an "Identification Kit". Here’s what you’ll need:- A piece of plain white paper (a blank specimen label works great.)
- Your fingernails (preferable still attached to your fingers!)
- A copper penny (or small –½ inch – piece of copper or short piece of heavy copper wire.)
- A small piece of fluorite (a broken cleavage piece is fine.)
- A pocket knife (NOT a Swiss Army knife – the steel in those is harder than in most cheap pocket knives, which can throw hardness tests off.)
- A small section of a steel file (a 2 or 3 inch tip from a triangular file for sharpening chain saws works fine.)
- A piece of a quartz crystal (with at least one good face and a sharp point - a broken section usually has a sharp point on it somewhere, it doesn’t have to be a crystal termination.)
- A small piece of a beryl or topaz crystal (with at least one good face and a sharp point or edge.)
- A small piece of a corundum crystal (with at least one good face and sharp point or edge.)
- A "streak plate" (unglazed porcelain tile – a 2 inch square is plenty.)
- A short candle stub and matches (in waterproof container) or a cigarette lighter.
- A small pair of tweezers.
- A small magnet (a refrigerator magnet is fine, but should be a fairly strong one.)
- A 10x hand lens/jeweler’s loupe.
- Blank specimen labels.
- Pens or pencils.
The items can be kept in a leather pouch, a small plastic box – or anything that’s the right size and durable. But it is a good idea to keep the kit items together in some sort of container. Then you always know where to find them when you need them.
[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]
Mineral Properties
Luster Hardness Streak Cleavage Fusiblity Specific Gravity Habit Tenacity Color Luminescence Radioactivity MagnetismIn order to use this Key and the test kit described above, you need to understand some basic principals of mineralogy. The most important are: luster, streak, hardness, and cleavage. It also good to know a bit about such things as specific gravity, fusibility, mineral "habits," and the types of mineral "environments" different minerals are likely to be found in – what types of rock, under what physical conditions. Brief discussions of the most important properties follow below. Any good mineral book should have more detailed sections discussing them, and the user of this Key is advised to get one and read it before working with this Key and the kit.
Luster: A mineral’s luster is the overall sheen of its surface – it may have the sheen of polished metal, or that of an unpolished metal that is pitted by weathering – or it may have the sheen of glass, or look dull or earthy, etc. Luster should not be confused with color: A brass-yellow pyrite crystal has a metallic luster, but so does a shiny grey galena crystal . Quartz is said to have a glassy (or vitreous) luster, but its color may be purple, rose, yellow, or any of a wide range of hues. The different types of luster referred to are: Metallic, having the look of a polished metal; Submetallic, having the look of a metal that is dulled by weathering or corrosion; and Non-metallic, not looking like a metal at all. Nonmetallic luster is divided into several sub-types:
- Adamantine, having the hard, sparkly look of a diamond
- Glassy/Vitreous, having the look of glass;
- Resinous, having the look of amber – not quite glassy;
- Pearly, having the iridescent look of mother-of-pearl (though usually just barely);
- Greasy/Oily, having the look of an oil-coated substance;
- Silky, having the look of silk, fine parallel fibers of mineral – such as chrysotile "asbestos;"
- Dull, having a plain looking surface that is not submetallic;
- Earthy, having the look of soil or clay.
Hardness is a mineralogical term denoting how resistant a mineral is to being scratched. It should not be confused with a mineral’s overall "toughness." (Diamond is the hardest known mineral, but it has a perfect cleavage and breaks easily along that cleavage.) Relative Hardness is used in identification by comparing the hardness of the mineral to that of items with known hardness. Mohs Scale of Relative Hardness is used, and is presented here with the addition of a few common materials of known hardness added:
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One tests for Relative Hardness by scratching the surface of a crystal or cleavage face with an item of known hardness – and vice versa, scratching the item of known hardness with a sharp point, edge, or grain of the mineral being tested. Whenever possible, the test should be done both ways – first trying to scratch the sample, then trying to scratch the item of known hardness, such as scratching a crystal face with a knife point and then trying to scratch the knife blade with the point or a sharp edge of the crystal. Since some minerals may leave a powdered streak on the item being scratched (or the known hardness item may leave a streak on the sample) one must rub the "scratch" with a finger to see if it is really a scratch or just a powder streak that rubs off. If a mineral produces a powder streak on the item being scratched then it is probably softer than that item. (Conversely, if the item leaves a streak on the sample it is softer than the sample.)
Since the "scratch test" is very important to the identification of
minerals every effort should be made to get a positive result – be sure
that the correct hardness is determined. With some samples, it may
take several tries before one can safely conclude the sample’s hardness.
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Streak is simply the color of a mineral powder. Many minerals have a different color when powdered than they do in crystal or massive forms. The color may be entirely different, or it may be a different shade. Quite a few minerals give a powder streak that is lighter in color than the whole crystal or massive pieces. A streak is usually obtained by dragging a sharp edge, grain, or point of a crystal across a streak plate – which is simply an unglazed piece of porcelain tile, such as those used in bathrooms and kitchens. (If you get your streak plate from a home improvement shop be sure what you get is unglazed porcelain – not plastic or some other material.) A porcelain streak plate has a relative hardness of about 6½. So minerals of that hardness and greater can not be tested on it – they’ll only scratch it. Some geologists use a file to test the streak of minerals with a hardness of 6 to 6½.
Streak plates tend to end up covered with traces of mineral powder in various colors. They can be "refreshed" by sanding them with fine emery sandpaper – 220 grit or higher. Do not use a coarser grit, as it will roughen the surface of the streak plate.
Some minerals can be difficult to get a good powdered streak from. As with other tests, repetition usually pays off. Always try to use a sharp edge or point, rather than just dragging the mineral across the streak plate willy-nilly. While some soft minerals give a streak easily no matter how you drag them, others will not streak well unless you use a small surface area of the mineral to get the streak. Get in the habit of looking for and using a sharp edge, grain, or the point of a crystal.
Return to Key: Step 4
Cleavage refers to the way some minerals break along certain lines of weakness in their structure. Mica is a good example – breaking along very closely spaced flat planes that yield thin "sheets." Calcite is another good example, breaking along three different planes that yield blocky fragments that look like a rectangular box that has been warped – called a "rhombohedron" or, simply, "rhomb." Galena breaks along three planes at right angles to one another, producing true cubes as fragments.
Cleavages are also described in terms of their quality: How smoothly and easily the mineral breaks. The qualities of cleavages are perfect, imperfect, distinct, good, fair, and poor. Mica is said to have a perfect cleavage (in one direction). Calcite has a perfect cleavage (in three directions). Feldspars – such as microcline – have a perfect cleavage in one direction and a good cleavage in another. Sphalerite has a perfect cleavage in six directions.
Cleavage may also be described in terms of crystallographic type:
- cubic (galena)
- octahedral (fluorite)
- rhombohedral (calcite)
- prismatic (feldspars)
- pinacoidal or basal (micas)
- etc.
The main thing that needs to be considered in the identification of minerals is whether or not a sample has a cleavage – many minerals don’t, breaking without producing smooth surfaces. Next is whether or not there are two or more cleavage surfaces present at angles to one another and, if so, the quality of the various cleavages. Where two or more cleavage surfaces are present, it then becomes important to figure out which crystal form they represent – cubic, prismatic, and so on. This is usually done by "guestimating" the angles between cleavage surfaces. Some are easy, like galena with its three perfect cleavages at 90 degrees to one another being cubic. Others can be hard to determine and may require measurement of the angles. A device called a contact goniometer can be handy for doing this. It is simply a protractor with an adjustable arm on it that is used to lay along one cleavage surface while the base of the protractor is laid across another. More information on this can be found in some field guides and most mineralogy texts. One can also make simple line drawings on a sheet of paper of the various angles common to minerals and keep the sheet in your guide. This can be used for making "eyeball comparisons" with the angles between cleavage surfaces on samples.
By-and-large, cleavages at 90 degrees to one another indicate a cubic form, cleavages at 120 and 60 degrees in the same sample indicate a rhombohedral form, and cleavages at acute to obtuse angles over long surfaces indicate a prismatic form – such as in feldspars. Nearly rectangular or sharp angles in prismatic minerals may indicate a Pyroxene Group mineral or one of the Feldspars, while more open angles – approximately 120 degrees – may indicate an Amphibole Group mineral. (Not all do, but these three groups are common and frequently seen, so seeing these types of cleavages is likely to mean you have one of them.) A single cleavage at 90 degrees to a crystal face indicates a basal form – such as in micas. See a good guide book for further information.
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Fusibility is a measure of how much heat it takes to melt a mineral into a globule, or at least to melt the sharp edge of a sharp splinter and make it round over. Quite a few minerals are easily fusible in the flame of a candle or typical cigarette lighter: A small, sharp, splinter held in the flame either melts into a globule or its edges round over easily. So this can be a handy test to do; a candle and matches or lighter are no big imposition. Such minerals are said to have a fusibility of "1" or "2" – though for our purposes the degree of difficulty with which a mineral fuses is not particularly important. Either it does or it doesn’t.
Other fusibility tests can be performed in the home workshop, using
a blowtorch. It takes some practice, but it should not be too hard
for most people to become proficient at these tests.
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Density and Specific Gravity are not properties easily determined, requiring special equipment; but a result of them, which might simply be called "heft" can come in handy: The denser a mineral is, the heavier it is per given volume. A 1 inch cube of galena is noticeable heavier in the hand than a 1 inch cube of pyrite. A barite crystal of the same size as other similar glassy crystals is likely to feel noticeably heavier. So do cerussite and anglesite crystals. So a mineral’s "heft" can be a clue to its identity. With a little practice a collector can become quite proficient at judging the relative weight of minerals and using that to help establish a sample’s identity.
In the home lab or workshop, specific gravity (S.G.) can be a very useful property in identifying minerals. Collectors should learn about S.G. and test for it routinely when working on ""mystery minerals" at home. Any good guide or text covers this topic and methods of testing. Probably the easiest is using a standard triple-beam balance, available from any scientific supply house – or perhaps through the local high school chemistry lab.
Habit is the general appearance a mineral tends to have – whether it is found as blocky crystals, long slender ones, or aggregates of some type, etc. If the crystals are glassy and cubic in shape you know they aren’t quartz. If they are rounded like a soccer ball you know they aren’t tourmaline. And so on…
Distinct crystals may be described as:
- Blocky or Equant – roughly box-like or ball-like, as in pyrite.
- Prismatic – elongated with opposite faces parallel to one another, in which case they may be short and stout, or long and thin.
- Bladed - Long thin crystals may be flattened like the blade of a knife;
- Acicular – needle-like;
- Filiform or Capillary – like hair or thread.
Groups of distinct crystals may be described as:
- Druzy – covering a surface in more-or-less outward pointing clusters of small crystals, such as druzy quartz crystals.
- Divergent or Radiating – growing outward from a point in sprays or starbursts, such as some hemimorphite exhibits.
- Reticulated – interconnected like a lattice or trellis, such as rutile.
- Dendritic or Arborescent – Slender divergent branch- or fern-like clusters, such as some native silver crystals.
- Columnar – stout parallel clusters with a column-like appearance, such as some forms of the serpentine minerals.
- Fibrous – aggregates of parallel or radiating slender fibers, such as chrysotile.
- Stellate – long thin crystals radiating outwards in all directions, like a starburst or in a circular pattern, such as astrophyllite.
- Spherical or Globular – compact clusters radiating outwards forming rounded, ball-like, shapes.
- Botryoidal – Globular or ball-like clusters – like a bunch of grapes – that do not have internally radiating fibers.
- Reniform – Radiating compact clusters of crystals ending in rounded, kidney-like, surfaces, such as hematite often exhibits.
- Mammillary – large rounded masses resembling human breasts.
- Foliated – looking like overlapping flakes or leaves and easily separable into individual leaves or flakes, usually at least somewhat "wavy" in appearance, such as the chlorite minerals.
- Micaceous – Like foliated, but splits into very thin sheets, like the mica minerals.
- Tabular or lamellar – Flat, platy, grains thicker than flakes or leaves, but overlapping like foliated, such as molybdenite.
- Plumose – Feather-like sprays of fine scales, similar to dendritic but with a much finer structure, such as one form of native silver.
A few other descriptive terms are:
- Massive – no crystal structure visible, though the mineral may be crystalline. Some massive minerals may also be granular.
- Banded – showing different bands or layers of color or texture, as in some agates or some fluorite.
- Concentric – in rounded masses showing layers around the mass in shells, working outward from the center, as in some agates.
- Pisolitic – roughly pea-size rounded masses.
- Oolitic – masses of small round spheres about the size of fish eggs.
- Geode – A rock with a hollow, roughly spherical, interior with concentric bands of mineral (usually agate) on the wall and possibly crystals on the interior surface, pointing inwards.
- Concretionary – masses formed by mineral being deposited around a nucleus, may be spherical or rounded but may also be a wide variety of other shapes.
Tenacity refers to a mineral’s resistance to breaking, bending, or otherwise being deformed. A mineral may be brittle, easily broken or crushed to powder; malleable, easily hammered into thin sheets (such as copper or gold); sectile, easily cut with a knife; flexible, easily bent without breaking and then staying bent; or elastic, bending but resuming its original shape once pressure is released.
Tenacity is particularly useful in telling some of the metallic minerals apart. Gold is malleable, pyrite (and most other look-a-likes) is not. Gold is also sectile and – in thin sheets – flexible. Galena is brittle, while platinum is malleable and sectile.
Flexibility and elasticity can be useful with minerals that are commonly found as flakes or acicular crystals. Chlorite flakes and thin crocoite crystals can be bent, and they will stay bent. Mica sheets bend and then snap back to their original shape when released.
Color is often a double-edged sword
in mineral identification: There are many minerals which have distinctive
colors; but there are also many which come in a variety of hues.
And the same color can be seen in several different species. So one needs
to use color as a criteria with care. That "malachite-green" mineral
may not be malachite… That brass-yellow metallic mineral may not
be pyrite… It is always a good idea to try and get a powdered streak
from any colored mineral and compare it with descriptions of the streaks
for the likely suspects you have in mind. It is also always
wise to consider the habit of the mineral in conjunction with the color.
A green prismatic crystal with a hexagonal cross-section is more likely
to be elbaite than malachite. A brassy wedge-shaped crystal is more
likely to be chalcopyrite than pyrite.
Color, in general, should never be taken as diagnostic by itself. While it may be for certain species, more likely than not it isn’t. Else the job of mineral identification would be made easy.
Play of Color can be more helpful than the color itself. Characteristics such as opalescence, iridescence, chatoyancy and asterism are peculiar to a limited number of species, or varieties of species.
Opalescence, as the word suggests, refers to an opal-like play
of light, reflections off the mineral
producing flashes of color that may appear somewhat like a patch-work
of different "grains" of color that aren’t really there: Move the
sample minutely and the color disappears from that spot. It is sort
of like taking a pearly luster to the nth degree.
Iridescence is similar to opalescence except that it is usually associated with metallic minerals and surface reflections rather than glassy minerals and sub-surface reflections: An exception is the type of iridescence known as labradoresence or schiller, found in labradorite and a very few other minerals.
Chatoyancy is the play of light off closely packed parallel fibers or parallel inclusions in cavities. The light reflects along lines – which may be straight or curved – giving the mineral a somewhat silky appearance. This characteristic is seen in such minerals as "satin spar" gypsum, "tiger’s eye" (fibrous crocidolite replaced by quartz), and chrysoberyl.
Asterism is a type of chatoyancy in which the fibers or inclusions reflecting the light are arranged in a pattern radiating outwards from a point producing a star-like pattern. This is most often seen in rubies and sapphires, and sometimes in phlogopite mica that has rutile inclusions.
Luminescence is the emission of light
by a mineral other than the reflected light of the sun or a lamp – the
mineral "glows" due to some other reason. The usual reason is reaction to ultraviolet light, though X-rays and cathode rays may produce it as well. The types of luminescence seen in minerals are fluorescence and phosphorescence – two closely related phenomena.
Fluorescence
results from electrons orbiting the mineral’s atoms being excited by ultraviolet light; the electrons "absorb" the energy and jump to higher orbits, then fall back to their original orbits – giving off light in the visible spectrum as they do. Phosphorescence is basically the same thing, but continues for a time after the source of excitation is removed, giving off energy as visible light more slowly. The fact is that most
fluorescent minerals exhibit phosphorescence to some extent, though
it usually can only be seen under careful lab conditions. Only a
very few minerals phosphoresce well enough to see in a simple darkened
room, and the phenomenon is usually rather short lived.
Fluorescence is a useful field identification tool for collectors who have UV lights (and a thick blanket when in the field) Many localities have at least a couple of fluorescent minerals, and some – like Franklin/Ogdensburg, New Jersey, USA – have a wealth of them. Where they are present, the UV light can be put to use in identifying them.
Radioactivity is another property that, while not too common, is found in some minerals and can be useful in identification. Collectors who have a Geiger counter may find it useful at certain localities, particularly pegmatites – where many of the more common radioactive minerals are found.
Magnetism is not too prevalent in minerals, but in those that do exhibit it the property can be useful in making an identification. Carrying a small but strong magnet in a field kit is a good idea, even if it only gets used now and then. The only strongly magnetic mineral collectors are likely to come across is, of course, magnetite. Some other minerals that may exhibit weak magnetism are pyrrhotite, ilmenite and franklinite.
A couple of other electrical properties found in minerals are piezoelectricity
and pyroelectricity,
though they are not common. They are also rather difficult to test
for and won’t be covered here. Anyone interested in them can
find information in most texts on mineralogy.
Luster Hardness Streak Cleavage Fusiblity Specific Gravity Habit Tenacity Color Luminescence Radioactivity Magnetism
[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]
Mineral Environments & Associations
Where a mineral is found – the type of rock in which it is found – and with what it is found – the other minerals that occur with it – can be as important to identifying the mineral as its physical properties. While there is not room for much of this information in the Key, the collector should pay close attention to it when they encounter it in field guides or other reference works.
Mineral Environments refers to the "geologic environments" in which minerals occur – the types of rocks in which they are found. While some minerals occur in two or more environments, others tend to be restricted to a single environment. If you think you have found the mineral kyanite in a sedimentary sandstone and see that it is a mineral formed by metamorphic processes you’ll know it can’t be kyanite. Try celestite… If you think you have found topaz in a cavity in basalt and read that it is largely restricted to pegmatite you’ll know it isn’t topaz. And so on.
On a smaller scale, environments can vary over the volume of a single deposit. A lode of copper ores may have an oxidized zone, a hydrothermal zone, and a deep primary zone. Each zone tends to produce distinct mineral assemblages. And figuring out what zone a mineral was created in leads to learning about mineral associations.
Mineral Associations are simply that – what minerals occur with one another in what environments. Such as minerals like malachite and brochantite most often being found with chalcopyrite and pyrite. Or secondary phosphate minerals being associated with triphyllite or lithiophilite. If you think you’ve found vivianite but there is no triphyllite around, maybe that isn’t what you have…
So it is always a good idea to pay attention to environmental information and any associations described. Sometimes an identification can be nailed down with that information – or one or more likely suspects eliminated by it. As stated above, this information is as important as the physical properties of the minerals themselves.
[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]
In Conclusion
As hinted at in the sections above, the collector needs to be careful about depending too much on any one or two properties or tests. While a mineral’s color, or hardness, or streak, etc., may suggest a likely culprit, a systematic approach – followed methodically – is much more likely to bring you to an accurate conclusion. Many collectors are well aware of the unreliability of "sight identifications" – deciding what a mineral is just by looking at it. Yes, many common minerals can be identified that way with experience – but many more can’t, and every now and then something so identified turns out to actually be something else. Even chemical and crystallographic tests have been known to fail to identify a mineral correctly. So it isn’t surprising that simpler techniques need to be used carefully in order to get the best results; and sometimes, they too fail.
Finally, while this Key should help the collector correctly identify many minerals, it won’t work all the time. Common minerals are found in uncommon forms. Some are closely mimicked by less-common or rare species. And, there is always the chance that a collector will find something that isn’t even covered by this Key. If you find yourself correctly identifying 60% of the minerals you find, you will be doing well. And the odds are that the other 40% are species not readily identified with this key – worked on in the home lab with other techniques, maybe even sent in to a professional lab in order to obtain a positive identification.
The trick is to do your best at each stage of the discovery process.
[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]
Organization & Redundancy
Beyond the obvious organization of the mineral listings into sections and sub-sections, there is a rough order of presentation which may help make it easier for the user to key things out.
The main order of presentation is by key features of the minerals – luster, streak, cleavage, and so on. When the key leads you to a particular sub-section based on a key feature you then have to carefully try and match your sample to one or more of the descriptions listed in that subsection. Since some of the subsections have quite a few minerals listed, an attempt has been made to organize them into groupings based on further refinements of the features. For example, if you have a non-metallic mineral with a colored streak and end up at subTable IIA you will see that the minerals are grouped according to color of streak – all the pinks to reds together, all the oranges and yellows next, and so on. Then within a particular group they are listed roughly in order of increasing hardness – softer ones first, hardest last. So you should be able to quickly eliminate anything that doesn't have the color streak of your sample and concentrate on those that do, and if you know the hardness you may be able to focus your search even further, paying closest attention to those species with the same hardness as your sample.
Another example is the way subTable IIB-1 is subdivided: all those that have cleavage in only one direction are first, then those with two cleavages, then those with three. Note that the background color in the table changes with each change in the number of cleavages. Within each group they are again listed in subgroups by color and hardness. So if you have a sample with cleavage in two directions you can quickly skip down to the listings for those and then home in by color and hardness. In places, the subdivisions go even further – like all the Amphibole Group species of similar hardness being listed together.
Several subsections are organized first on Cleavage. In the tables you will note that different background color bands are used with different numbers of cleavage directions. Thus, if you have a sample in which you see three directions of cleavage, it is easy to quickly skip over the minerals with only one or two directions of cleavage and go directly to the group which has three.
Hopefully this organization – which is admittedly not perfect – will help you to refine your search and focus on the most likely minerals that match the sample in your hand.
A number of minerals are listed in more than one place. For example, hematite is listed three times. This is because it has such varied habit and differences in its properties from habit-to-habit that one might key one sample out to one place, but then key out a sample with a different habit and properties to another place. Also, some species sort of fall on the dividing line between sections of the listings. Such minerals might key out to either section, so they are listed in both. And some species may or may not exhibit prominent cleavage, keying out to different spots depending upon which is the case for the sample you have in your hand. Etc…
Hopefully this feature of the key will enhance the odds of keying out any given sample – no matter what it's particular properties may be.
Table of Contents The Mineral ID Key
| The Mineral Identification Key |
Step 1: Is the Luster Metallic or Submetallic?
- [Go to Section I: Metallic or Submetallic Luster Key, Step 2]
- [Go to Section II: Nometallic Luster Key (Soft), Step 4]
Section I: Minerals with a Metallic or Submetallic Luster
Step 2: Will the mineral leave a mark on paper? (Hardness less than 2½?)
- [Go to Table IA]
- [Go to Step 3]
Table of Contents Step 1 Hardness
Section I: Minerals with a Metallic or Submetallic Luster & Hardness Greater than 2½
Step 3: Can the mineral be scratched by a knife? (Hardness less than 5½?)
- [Go to Table IB]
- [Go to Table IC]
Table of Contents Step 1 Step 2 Hardness
Section II: Minerals with a Non-Metallic Luster
Step 4: Does the mineral have a definitely colored streak? (Leaves a colored powder streak on unglazed porcelain?)
[Go to Table IIA]
[Go to Step 5]
Table of Contents Step 1 Step 3 Streak
Section II: Minerals with a Non-Metallic Luster
Step 5: Can the mineral be scratched by a fingernail? (Hardness less than 2½?)
[Go to Step 6]
- [Go to Step 7]
Table of Contents Step 1 Step 4 Hardness
Section II: Minerals with a Non-Metallic Luster & Hardness Less than 2½
Step 6: Does the mineral have prominent cleavage?
- [Go to Table IIB-1]
- [Go to Table IIB-2]
Table of Contents Step 1 Step5 Cleavage
Section II: Minerals with a Non-Metallic Luster & Hardness Greater than 2½
Step 7: Can the mineral be scratched by a copper penny? (Hardness less than 3?)
- [Go to Step 8]
- [Go to Step 10]
Table of Contents Step 1 Step5 Hardness
Section II: Minerals with a Non-Metallic Luster & Hardness Greater than 3
Step 8: Does the mineral have a prominent cleavage?
- [Go to Table IIC-1]
- [Go to Step. 9]
Table of Contents Step 7 Cleavage
Section II: Minerals with a Non-Metallic Luster, Hardness Greater than 2½ & No Prominent Cleavage
Step 9: Will a thin splinter fuse in a candle flame? (Fusibility of 1?)
- [Go to Table IIC-2a]
- [Go to Table IIC-2b]
Table of Contents Step 8 Fusibility
Section II: Minerals with a Non-Metallic Luster & Hardness Greater than 3
Step 10: Can the mineral be scratched by a knife? (Hardness less than 5½?)
- [Go to Step 11]
- [Go to Step 12]
Table of Contents Step 7 Hardness
Section II: Minerals with a Non-Metallic Luster & Hardness Less than 7
Step 11: Does the mineral have a prominent cleavage?
- [Go to Table IID-1]
- [Go to Table IID-2]
Table of Contents Step 10 Cleavage
Section III: Minerals with a Non Metallic Luster & Hardness Greater than 5½
Step 12 Can the mineral be scratched by a sharp quartz point? (Hardness less than 7?)
- [Go to Nonmetallic Luster Key (Hard): Step 13]
- [Go to Nonmetallic Luster Key (Hard): Step 14]
Table of Contents Step 10 Hardness
Section III: Minerals with a Non Metallic Luster & Hardness Less than 7
Step 13 Does the mineral have a prominent cleavage?
- [Go to Table IIIA-1]
- [Go to Table IIIA-2]
Table of Contents Step 12 Cleavage
Section III: Minerals with a Non Metallic Luster & Hardness Greater than 7
Step 14 Does the mineral have a prominent cleavage?
- [Go to Table IIIB-1]
- [Go to Table IIIB-2]
Table of Contents Step 12 Cleavage