Tourmaline on Lepidolite with Quartz

Tourmaline
Complex Borosilicates, (Na,Ca)(Mg,Fe2+,Fe3+,Al,Li)3-Al6 (BO3)3Si6O18(OH)4
Crystal System: Hexagonal
Hardness: 7.0
Density: 3.0-3.3

Tourmaline is represented by a group of minerals having complex compositions which are generally represented by the above formula. Elbaite, schorl, buergerite, dravite, uvite and liddicoatite are members of the tourmaline group. The most common member is the black, iron-bearing schorl.

Tourmaline is a mineral of widespread occurrence and is found in granite pegmatites, pneumatolytic veins and granites. It also occurs as a product of metasomatism involving boron.

Tourmaline occurs as transparent to translucent elongated, prismatic crystals in aggregates of parallel or radiating crystals. The two ends of a single crystal are sometimes terminated differently. Enormous crystals have been found. Tourmaline occurs less frequently as stubby prismatic crystals or compact masses. It often exhibits a vitreous luster and is remarkably variable in color, ranging from colorless to blue, pink, yellowish green, green, brown, bluish black, and black. Some crystals are pink at one end and green or black at the other. These different zones of color are due to the time the material has taken to crystallize, with different tinctural agents effecting the crystal at different times during the formative process.

The individual colors are due to the presence of one or more of the following elements acting as chromophores: chrome, copper, iron, manganese, titanium and vanadium. Copper produces blues, chrome and vanadium produce greens, manganese produces pinks and reds, titanium produces browns, while iron in various oxidation states can play a role in producing greens, blues and reds in various tourmaline species. Mixing of these chromophores can produce other colors, such as yellow-green produced by titanium mixed with manganese and low iron.

Lepidolite
Potassium Lithium Aluminum Silicate Fluoride Hydroxide, K(Li,Al)3(Si,Al)4O10(F,OH)2

Lepidolite is a member of the mica group. It is a typical constituent of lithium-bearing granite pegmatites and is associated with spodumene and amblygonite.

Quartz
Silicon Dioxide, SiO2
Crystal System: Hexagonal
Hardness: 7.0
Density: 2.65

Quartz is by far the most abundant of the polymorphic forms of silica and the most widespread and abundant mineral, making up 12% of the earth's crust by volume. It occurs in igneous, metamorphic and sedimentary rocks as well as hydrothermal veins, metasomatic and hot spring deposits. Quartz crystals are found as a common gangue material in veins of many minerals and in cavities in granite porphyries and pegmatites.

Quartz is transparent and colorless when pure, and such clear material is known as rock crystal. When impurities are present in the crystals, a very wide range of colors is exhibited by quartz, which include purple (amethyst), white (milk quartz), pink (rose quartz), yellow (citrine), and brown to black (smoky quartz). Included materials such as hedenbergite, rutile, tourmaline, or zoizite can cause quartz to appear green, blue, red or yellow. Impurities and inclusions cause quartz crystals to vary from transparent to opaque.

Quartz is also extremely variable in form, and may occur as well formed, elongated, hexagonal, prismatic, and sometimes enormous crystals; in compact and concretionary masses; and in microcrystalline and cryptocrystalline forms.

The faces of prismatic crystals may exhibit horizontal striations with randomly corroded edges. Prismatic crystals are often terminated by two rhombohedra of opposite polarity. Quartz crystals are often twinned, with dauphine twins being the most common twinned form, followed by Brazil and Japan Law twins in occurrence. Scepter crystals, where a new quartz crystal forms over and caps a previously formed prismatic crystal, are rarer. Quartz crystals are rotary polar and occur as left or right handed crystals, as determined by the spiral structure of linked silicon-oxygen tetrahedra in the crystal. Bubbles of gas or liquid are often present and evident at the microscopic and macroscopic levels in quartz crystals.

Chalcedony is a microcrystalline variety of quartz that is of interest to may rockhounds who do lapidary work. Most chalcedony occurs as precipitates of silica bearing solutions and forms in cavity linings, veins and precipitated masses in a variety of rocks. Chalcedony also occurs as a dehydration product of opal. Types of chalcedony include banded agate, moss agate, jasper, onyx, carnelian, chrysoprase, chert, flint, heliotrope (blood stone), plasma and sard.

Quartz is a very important industrial material and many useful applications exist for it. It's piezoelectric properties are widely used in electronics as pressure sensors an oscillators. Quartz is the raw material used in the manufacture of silicon carbide, a widely used industrial abrasive. Quartz also finds many applications in optics. Quartz crystals have the ability to rotate the plane of polarization of light and it's transparency finds applications in heat lamps, prisms, lenses and optical windows and flats.

Stuart provides the following remarks:

"This is one of my favorite Tourmaline localities, the Jonas Mine. It produced what is commonly today known as Rubellite Tourmalines. This refers to the rich deep cranberry red color which is virtually unmatched by any other locality. This mine produced the largest gem quality rubellites ever found. The largest being aptly named 'The Rocket' which stands over 5 feet tall and has been valued in the many millions of dollars."


Rocks from Stuart Wilensky's Collection

Index of Specimen Images

Table of Contents

bkeller@rockhounds.com 8/8/95