index mineral การใช้

• Staurolite is a common metamorphic intermediate-grade index mineral.
• Minerals that are characteristic for a certain metamorphic grade are called index minerals.
• Often they are named for the most characteristic index mineral of the zone.
• Many index minerals have complicated chemical compositions.
• Index minerals are used in geology to determine the degree of metamorphism a rock has experienced.
• Whether a certain index mineral occurs is also dependent on the composition of the rock itself.
• Lawsonite is a significant metamorphic mineral as it can be used as an index mineral for high pressure conditions.
• Every first appearance of an index mineral was taken by Barrow as the beginning of a new metamorphic zone.
• Very typical index minerals are the polymorphs of aluminosilicate ( Al 2 SiO 5, all are nesosilicates ).
• These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet.
• The first or last appearance of an index mineral ( the place where a metamorphic reaction is observed ) forms an easily recognizable isograd.
• Thus, as with its other polymorphs, andalusite is an aluminosilicate index mineral, providing clues to depth and pressures involved in producing the host rock.
• This new mineral that is produced in the metamorphosed rock is the index mineral, which indicates the minimum pressure and temperature the protolith must have achieved in order for that mineral to form.
• Andalusite, kyanite, and sillimanite are naturally occurring aluminosilicate minerals that have the composition polymorphs is located at a temperature of 500 癈 and a pressure of 0.4 GPa . These three minerals are commonly used as index minerals in metamorphic rocks.