THE MINERAL HINSDALITE

Hinsdalite is a difficult mineral to classify in that it has both a phosphate anion group and a sulfate anion group. The phosphate anion group would normally dictate that hinsdalite be classified in the Phosphate Class of minerals. But hinsdalite's sulfate anion is intricate and essential in its structure, while the phosphate anions can be substituted for to at least a limited degree, by other anion groups. Some other classification schemes may place hinsdalite in the Phosphate Class however.

PHYSICAL CHARACTERISTICS:

• Color is yellow, golden-yellow, greenish yellow, green to colorless.
• Luster is vitreous to greasy.
• Transparency: Specimens are mostly translucent to small crystals being transparent.
• Crystal System is trigonal.
• Crystal Habits include pseudocubic and pseudotetragonal rhombohedrons and modified rhombohedrons. Clusters of spherical flakes and tablets are known. Faces tend to be curved and striated. Granular or massive formations are also seen.
• Cleavage is perfect in one direction (basal).
• Fracture: Uneven.
• Hardness is 4.5.
• Specific Gravity is approximately 3.7 (above average for non-metallic minerals).
• Streak is white.
• Associated Minerals include chalcocite, galena, pyrite, sphalerite, covelite, bornite, pyrophyllite and quartz.
• Notable Occurrences are limited to the type locality at the Golden Fleece Mine, Lake City, Hinsdale County (hence the name), Colorado as well as locations at Butte, Montana; Ithaca Peak Mine, Mohave County, Arizona and Slate Mountain, El Dorado County, California, USA.
• Best Field Indicators are crystal habit, color, hardness, density and locality.