1911 Encyclopædia Britannica/Hiddenite

HIDDENITE, a green transparent variety of spodumene, (q.v.) used as a gem-stone. It was discovered by William E. Hidden (b. 1853) about 1879 at Stonypoint, Alexander county, North Carolina, and was at first taken for diopside. In 1881 J. Lawrence Smith proved it to be spodumene, and named it. Hiddenite occurs in small slender monoclinic crystals of prismatic habit, often pitted on the surface. A well-marked prismatic cleavage renders the mineral rather difficult to cut. Its colour passes from an emerald green to a greenish-yellow, and is often unevenly distributed through the stone. The mineral is dichroic in a marked degree, and shows much “fire” when properly cut. The composition of the mineral is represented by the formula LiAl(SiO₃)₂, the green colour being probably due to the presence of a small proportion of chromium. The presence of lithia in this green mineral suggested the inappropriate name of lithia emerald, by which it is sometimes known. Hiddenite was originally found as loose crystals in the soil, but was afterwards worked in a veinstone, where it occurred in association with beryl, quartz, garnet, mica, rutile, &c.