chiastolite

thumb|260px|Specimen from Santiago de Compostela, Spain

Chiastolite ( ) is a variety of the mineral andalusite with the chemical composition Al2SiO5. It is noted for its distinctive cross-shaped black inclusions of graphite. The presence of these crosses caused the mineral to be used as a gem. Chiastolite specimens were distributed throughout Europe from the 16th century, as an amulet or souvenir provided by the pilgrims returning from Santiago de Compostela (Saint James of Compostella), in Spain. When chiastolite appears in the old books of mineralogy, it is cited with the name of lapis crucifer or lapis cruciatur, cross stone. The first figure of a chiastolite appears in Laet's book De Gemmis et Lapidibus, published in 1648. The chiastolite specimens sold to the pilgrims came from Asturias, where it is very abundant, in large specimens, in the area of Boal.