THE MINERAL SCHMITTERITE

Chemistry: (UO₂)TeO₃, Uranyl Tellurite
Class: Sulfates
Subclass: Tellurates
Uses: Only as mineral specimens.
Specimens

Schmitterite is a very rare tellurium mineral. The type locality for schmitterite, Moctezuma Mine, Moctezuma, Sonora, Mexico, is famous for rare telllurium minerals. Chemically schmitterite is doubly noteworthy as it is also a uranyl mineral. The uranyl ion group, UO₂, is unusual in that it is positively charged (+2). Most ionic groups, especially those that contain oxygen are negatively charged such as the sulfate ion group, SO₄^-2; carbonate ion group, CO₃^-2; borate ion group, BO₃^-3; phosphate ion group, PO₄^-3; tellurite ion group, TeO₃^-2 and the silicate ion group, SiO₄^-4. Because the uranyl ion group is positively charged some minerals do not require isolated metal ions and are thus composed of only ion groups such as the uranyl ionic group and the tellurite ionic group of schmitterite. Another positively charged ion group is the ammonium ion group, NH₄⁺¹, found in the minerals sal ammoniac, cryptohalite, tschermigite guanine, struvite and larderellite to name a few. Schmitterite is a radioactive mineral and should be stored away from minerals that are affected by radioactivity and of course human exposure should be limited.

THE PHYSICAL CHARACTERISTICS:

Color is colorless to yellowish.
Luster is pearly.
Transparency: Crystals are transparent to translucent.
Crystal System is orthorhombic; 2/m 2/m 2/m.
Crystal Habits include small granular crystals and massive.
Cleavage is good in one direction.
Hardness is 1.
Specific Gravity is approximately 6.8 - 6.9 (very heavy for translucent minerals).
Streak is white.
Other Characteristics: Specimens are somewhat radioactive.
Associated Minerals include various other tellurium minerals such rodalquilarite, emmonsite and other tellurates and tellurites.
Notable Occurrences are limited to the type locality of Moctezuma Mine and the Bambollita Mine of Moctezuma, Sonora, Mexico.
Best Field Indicators are locality,softness, high density, luster, radioactivity and cleavage.