By Jim Brace-Thompson
Many minerals crystallize in patterns that resemble across, a shape that has held special significance in Christian and pre-Christian civilizations. Two minerals that produce cross-shaped crystals—namely chiastolite and staurolite—have entered the realm of gemstone lore and legend as “fairy crosses.” Such crosses are said to be good luck charms, or talismans, that protect against witchcraft, illness or disaster. There are also Cherokee legends in North America of the Yunwi Tsunsdi, or Little People, who shed cross-shaped tears.
Destination Discovery Fuels Naming
Chiastolite is a variety of the mineral andalusite. Andalusite is named for Andalusia, Spain, the locality in which it was first found some 2,000 years ago. The word “chiastolite” is from the Greek word chiastos, or “cross”. When cut in cross-section, chiastolite crystals reveal a pattern that resembles an iron cross. They are sometimes worn as charms, either polished or in their natural form. Mariposa County, California, is home to an especially famous and prolific locality. Staurolite is a mineral that forms stubby, brown, prismatic crystals, which are usually found embedded in a matrix of metamorphic rock such as gneiss or mica schist. Staurolite has a tendency to “twin”, or have intergrown pairs of crystals.
There are two kinds of mineral twins: contact and penetration. Contact twins grow side by side, producing crystals that are mirror images of one another. Penetration twinned crystals cut across each other.
Staurolite often forms penetration twins that are called cruciform twins, since they resemble crosses. “Staurolite” comes from the Greek words stauros and lithos, meaning “cross stone”. In the United States, famous deposits are located in Minnesota, Tennessee, New Mexico, Virginia, and especially Georgia, where staurolite has been designated the state mineral.