It's no wonder marble
is so widely used in buildings, sculptures and anything else
imaginable. It's a perfect rock to use because it's soft - the white
mineral that dominates it is not quartz but calcite. It can form
either by regional metamorphism, or contact metamorphism near igneous
intrusions. Minerals other than calcite include tourmaline, epidote,
spinel, garnet, anorthite, albite, tremolite, diopside, pyrite,
graphite, mica and iron oxides. Depending on the exact mineral
composition, the rock can vary between grey, green, olivine and other
marble.
Quartzite,
on the other hand, is a hard rock that consists of the hard mineral quartz. It is formed
from sandstone - a quartz-rich rock. Metaquartzite contains over 90%
quartz. Other minerals include mica, feldspar and iron oxides. Both can
be formed by regional metamorphism, or contact metamorphism near an
igneous intrusion.
Amphibolite
Amphibolite. By Ron Schott via Flickr.com
Amphibolite
is a coarse-grained rock that most often forms by metamorphism of mafic
igneous rocks. The dominating mineral is amphibole, most often
hornblende. Others include garnet, epidote, chlorite, pyroxene and
feldspar. Garnets are common porphyroblasts. Amphibolite can have
foliation or schistosity.
Eclogite
Eclogite. By GOC53 via Flickr.com
Eclogite
forms at extreme temperatures and pressures from mafic igneous rock. It
is medium to coarse grained, typically greenish grey and often has
minerals like kyanite and red garnet. The greenish mineral is omphacite
- a type of pyroxene. it can occur as large rock bodies, or
as nodules in basalts and kimberlites. Eclogite is one of Eskola's
metamorphic facies.
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