29 No. 3
Stamp Your Crystallographer Would Like
and gems are depicted on a relatively large number of stamps
due to their inherent beauty, natural abundance, or commercial
value. There are at least a dozen different stamps showing
attractive samples of pyrite, quartz, or malachite, and many
more illustrating diamonds or gold. However, particularly
appealing to me are those stamps that portray less conspicuous
elements or minerals, especially when pertinent information
like the corresponding name or chemical formula is indicated
too. A beautiful example can be seen on the stamp that accompanies
this note and features a specimen of scheelite, one of the
common mineral ores of tungsten.
First identified in 1821, scheelite is a calcium tungstate (CaWO4) and is often found as relatively large golden yellow or orange crystals. Notable sources of this mineral are located in Australia, Austria, Bolivia, Brazil, the Sichuan province in China, England, Finland, France, Italy, Japan, the Tong Wha mine in South Korea, Myanmar, Sri Lanka, Sweden, Switzerland, and the United States. It was named after the famous Swedish chemist Carl Wilhelm Scheele (1742–1786), who discovered tungsten independently from the d’Elhuyar brothers in Spain among many other accomplishments. For example, Scheele is partially credited with the discovery of oxygen and chlorine, which he actually achieved before—but unfortunately published after—the isolation of these elemental gases was reported by Joseph Priestley and Humphry Davy, respectively.
Remarkably, the Peruvian stamp pictured herein not only includes the name and chemical formula of the mineral but accurately shows that it crystallizes in the tetragonal system, which can be regarded as an elongated cube (i.e., a rectangular prism with a square base [thus, a = b ≠ c] and right angles between the three crystallographic axes [α = β = γ = 90°])!
Written by Daniel Rabinovich <email@example.com>.
last modified 15 June 2007.
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