amblystine

Amblystine is a rare mineral belonging to the amphibole group, characterized by its dark green to black color and its prismatic crystal habit. It was first discovered in 1874 in the Amblystegos mine in the Swiss Alps, from which it derives its name. Amblystine is typically found in metamorphic rocks, such as schists and gneisses, and is often associated with minerals like tremolite, actinolite, and chlorite.

The chemical composition of amblystine is complex, with the general formula (Na,Ca)2(Mg,Fe)5Si8O22(OH)2. This formula indicates that amblystine contains sodium and calcium in its A-site, magnesium and iron in its M1 and M2 sites, and silicon and oxygen in its tetrahedral and octahedral sites, respectively. The presence of hydroxide ions (OH-) in its structure contributes to its dark color.

Amblystine's optical properties include a pleochroism that ranges from dark green to black, and it exhibits a distinct prismatic cleavage. Its hardness on the Mohs scale is approximately 5 to 6, and its specific gravity is around 3.2 to 3.4. Amblystine is not commonly used in jewelry due to its rarity and the difficulty in finding specimens of sufficient size and quality. However, it is of interest to mineral collectors and researchers due to its unique composition and the geological contexts in which it is found.