As a kid I was fascinated by the Golden Nature Guide to Rocks and Minerals, otherwise known as the little Zim book. I was enchanted by its pictures and text, also by its section on blowpipe tests, and thought someone who could do such tests must be great. The next book was that by Pough, which also mentions the tests, but as they are not illustrated there they are too often passed over, although results are available under “Tests” in each mineral entry. But when I was given a collection, along with an old blowpipe, platinum wire, spatula, charcoal block, and some stuff I have since forgotten, I got interested in chemistry and started to experiment. I still have the spatula, but have since worn out the blowpipe, platinum wire, and charcoal block, but not until I had gotten launched into a fascinating aspect of collecting minerals: Identification.

The pictures in the little Zim book are not for diagnosis, but were a fascinating introduction. I have since gotten other books, but keep a Zim book for the fun of it. The colors of tests can be fascinating. The bead tests are appreciated for their beauty, but any simple tests that work are used, and several are handy used prior to bead tests – particularly the tube tests, which help identify those elements, mostly the semi-metals, that are not used in bead tests as they can make brittle the platinum wire (Martin, 2002).

Some minerals when heated and oxidized on the charcoal block yield an oxide coating, either white or colored, depending upon the material. The use of certain fluxes can bring out other colors. For example, if a coating is yellow when hot and white when cold, it could be oxide of tin or zinc (oxide of Ti can be yellow also). One drop of solution of cobalt nitrate dropped onto the coating, the coating then subjected to the oxidizing flame again, then let cooled, may yield a green color. The shades of green are different for tin and for zinc, and they are easily distinguished once tried and learned. Sometimes impurities can affect the colors of the coatings, for example, sphalerite containing a bit of cadmium may cause a coating to be yellow when hot but pale yellow when cold. Some might confuse this color with another element, but sphalerite is distinguished from galena by a careful inspection of its cleavages, using a hand lens, before resorting to destructive testing (it is recommended to get as much information about the sample, examining it with magnification, before such testing). Further details are in the books, and as this article describes neither techniques nor results, but only introduction plus a few hints, one is better served by getting the books and using them, and trying the tests on known materials and learning them. However, a few hints not always included in the books are included here.

The method of using the blowpipe is not detailed here, but is in Brush, which one will want a copy anyhow. Safety hints are also not given here, as it is expected that anyone testing should learn proper safety procedures, as one should before performing any task, and use the proper ventilation procedures. Ventilation is a concern when subjecting certain minerals to heat and oxidation. In some cases positive outflow ventilation should be installed and used. However, if one uses tube tests before using charcoal block tests, one may identify many of the more volatile materials by tube tests instead (Martin, 2002).

Many metallic minerals yield reactions when heated in the oxidizing flame or in the reducing flame of the blowpipe, when the sample is on a charcoal support. Usually a shallow hole is made near one end of the charcoal block, the sample is placed in it, and the sample subjected to the flame, either an oxidizing flame or a reducing flame. In some cases soda (sodium carbonate) as a flux is mixed with the powdered sample. To keep the sample from blowing away under the flame, it can be wettened slightly which may hold it together until it works. Sometimes a bit of borax is added to the soda to help keep the sample/flux mixture from sinking into the charcoal.

Fusibility is mentioned in the books. A few minerals are easily fusible. A splinter of stibnite will fuse in a match flame. Many borates are also easily fusible. But many minerals require fusion in a blowpipe flame on the charcoal block. The books often picture fusing a splinter of sample held by platinum-tipped forceps, but as such a tool thus equipped (by platinum) is no longer available, and as most forceps act as heat sinks, making fusion more difficult, fusions are best done on the charcoal block. Also, as the blowpipe flame is small and has only so much heat, the size of sample matters, as a larger piece of the same mineral will not fuse as well as a smaller piece. Usually a size in the range of 1-mm or 2-mm will work. A hand lens is useful to inspect the fragment before and after the test.

An oversimplification of descriptions of fusibility are terms such as “fuses with ease” or “fuses with difficulty.” This may depend upon size of sample. The terms originally referred to positions on the fusibility scale. One method is to fuse a tiny bit next to an equally-sized bit of a mineral of a known fusibility, such as almandine garnet which is one of those on the fusibility scale. If both samples get treated equally by the same flame, one may make comparisons between their fusibilities.

Decrepitation, or the bursting into pieces in the heat, can be a nuisance (and a good reason for eye protection). One cause may be due to tiny inclusions of water which turn to steam and burst the fragment. If decrepitation occurs, one may first heat the powder in a test tube to contain the pieces until it ceases, and then test the powder.

Some samples after treatment, particularly if in the reducing flame, become magnetic (this may indicate Fe, Co, or Ni). Sometimes a tiny bead of metal is formed. This is usually when a flux, such as soda, is used, and then the bead of metal must be looked for within the flux.

Brush, also Pough, give discussion of testing and techniques, as well as results. Miners Catalog is a source of charcoal blocks, blowpipes, platinum wire, and such. Before RockNet deleted all entries dated before 7/01/01, there were some good posts on blowpiping by Al O. Maybe Al O. could contribute something further someday in this line as his posts were so interesting.

References:
Al O., 2001, The Flame and Blowpiping, 2/13/01 & 3/05/01 on RockNet (this may have been reposted 6/17/01), all now gone to wherever went other posts of dates before 7/01/01.
BRUSH, George J., 1890, Manual of Determinative Mineralogy...and Blow-Pipe Analysis. (any edition, whether of Brush or also of Penfield, is fine. Check used book dealers, or try the internet, either used book services, or simply search by title or author).
MARTIN, 2002, Tube tests for metallic minerals, 5/18/02, on RockNet, at www.rockhounds.com/rockshop/ rocknet_archives/messages/18299.html
MARTIN, 2002, Bead Tests, 6/19/02, on RockNet, at www.rockhounds.com/rockshop/scripts/rocknet/messages/19247.html
MINERS Inc., Catalog, P.O. Box 1301, Riggins, Idaho 83549-1301 (www.minerox.com)
POUGH, Frederick H., 1976, A Field Guide to Rocks and Minerals (any edition will do)

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From Martin - October 18, 2002 at 18:07:26
Email: dmartinm[ ]eudoramail.com