1. Staurolite is a common metamorphic intermediate-grade index mineral . 2. Minerals that are characteristic for a certain metamorphic grade are called index minerals . 3. Often they are named for the most characteristic index mineral of the zone. 4. Many index minerals have complicated chemical compositions. 5. Index minerals are used in geology to determine the degree of metamorphism a rock has experienced.6. Whether a certain index mineral occurs is also dependent on the composition of the rock itself. 7. Lawsonite is a significant metamorphic mineral as it can be used as an index mineral for high pressure conditions. 8. Every first appearance of an index mineral was taken by Barrow as the beginning of a new metamorphic zone. 9. Very typical index minerals are the polymorphs of aluminosilicate ( Al 2 SiO 5, all are nesosilicates ). 10. These minerals, known as index minerals , include sillimanite, kyanite, staurolite, andalusite, and some garnet.
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