Lepidolite: the Purple Mica

Lepidolite is part of a group of minerals known as the micas, which I have written about before. I have chosen to cover lepidolite separately because it has a few unique properties, the most noticeable being its attractive color.

Ultimately, what sets lepidolite apart from the other micas is the presence of lithium in its chemical structure. In fact, one of the more common types of mica, muscovite, can be turned into lepidolite under the right conditions if lithium is present.

Lepidolite shares many traits with the other micas, but its individual chemical structure imparts a few properties that the others cannot claim. Like its cousins, lepidolite’s crystals are six-sided, very flat, and so soft that they are usually distorted. The crystals are often grouped as stacks and they’re commonly found as flakes. The thin crystals or flakes are flexible, a characteristic which is rare in the mineral kingdom. Lepidolite has a vitreous to pearly luster and a Mohs hardness of only 2.5 as do the other mica minerals.

Lepidolite’s first visible property that differs from lithium-free mica is its violet color, though it can take pale pink, or rarely gray or yellow. And it can be triboluminescent (when pressed it will emit little flashes of light in the dark.)

Lepidolite was once used as an ore of lithium, but the lithium content varies in lepidolite so people found other sources of the metal. Lepidolite is found chiefly within rock formations called “granite pegmatites” in places like: Madagascar, Sweden, the Brazilian state of Minas Gerias, and the American states of California, Connecticut, and Maine.

Stibnite: Toxic Beauty

The metal antimony was once called stibium, which is why it is represented by an Sb on the Periodic Table of Elements. Stibnite’s name stems from the fact that it is an ore of antimony.
Stibnite is a steel-gray or lead-gray mineral that has a metallic luster (although it can tarnish, turning black) Stibnite’s crystals are orthorhombic and are usually blade or needle-shaped. Its crystals are slightly flexible so they can be bent or twisted. I wouldn’t do this with any good specimen, but it could be a helpful test to help identify the mineral. Stibnite measures only a 2 on the Mohs scale of hardness.
Stibnite is still the main ore of antimony, which has been used since ancient times (though for many years it was confused with lead) Today antimony is mixed with other metals to form alloys that are used as coverings for cables and in car batteries. Stibnite itself is used in the making of matches, percussion caps, and fireworks.
Stibnite is found in places like: Japan, Serbia, Macedonia, Romania, Peru, California, and Nevada.
A final word of caution: stibnite is a poisonous mineral! Antimony is toxic and it imparts this property to its ore. Always wash your hands carefully after handling stibnite. This topic will be discussed further in my next post.