Other orthosilicates include zircon, staurolite, and topaz. In the upper segment are different types of mica schist, granite, kyanite and staurolite. Minerals such as staurolite, andalusite and garnet are commonplace in these older formations. Orthoclase, staurolite, pyrite, and fluorite often show penetration twinning. It occurs associated with staurolite, andalusite, sillimanite, talc, hornblende, gedrite, mullite and corundum. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet. In handsamples, macroscopically visible staurolite crystals are of prismatic shape. Staurolite is a common metamorphic intermediate-grade index mineral. Staurolite is most commonly found in Fannin County, Georgia. Staurolite is a regional metamorphic mineral of intermediate to high grade. Staurolite often occurs twinned in a characteristic cross-shape, called cruciform penetration twinning.