Page 20 - Curriculum Visions Dynamic Book

Garnets, zircon and olivine
In these silicates the silica molecules are held together by metal atoms. This influences the shape of the crystals in each mineral.
The minerals in this group form at very high temperatures and are only in rocks associated with volcanoes and mountain-building.
Two of the more easily recognised are
garnet and zircon. However, the most widespread of these minerals is called olivine, a mineral found in all dark-coloured igneous rocks.
Garnet
Garnets are common minerals, varying in colour from green and yellow to deep, rich red. All crystal varieties within the group have a cubic shape.
Garnets are combinations of iron and silica with various combinations of calcium, aluminium and manganese. The various metals are responsible
for the variety of colours. Garnets are all hard and
have a glassy lustre. They are formed in granites but are especially common in rocks that have been subjected
to considerable heat
and pressure (known as metamorphic rocks), where
they form crystals much
harder than the surrounding rock. Weathering of rocks causes the garnets to protrude and become easy to spot. One of the most common of these rocks is a metamorphic rock called schist.
 Garnets are often found as single cubic crystals with a characteristic opaque pink colouration. Garnetiferous mica– schist is a common metamorphic rock. The majority of the rock
is made of mica crystals, which gives it its sheen; individual small transparent red garnet crystals grow in the mica.
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