Staurolite is a neosilicate mineral that is generally reddish-brown to black in color. Common in metamorphic rocks, such as quartzite, staurolite often forms in such a way that its prismatic crystals are twinned, giving them the appearance of a cross. Due to this unusual manifestation, the mineral has been revered as a good luck charm since antiquity when it was referred to as lapis crucifer, or cross stone. Some also call samples of the mineral fairy crosses, and, according to one legend, the tears of fairies that mourned the crucifixion of Christ formed the crosses.