When it forms transparent crystals it is called rock crystal.
Quartz is a silicon dioxide, which most often comes in this, colourless
and transparent form. It belongs to the group of tectosilicates. The
crystals are hexagonal or trigonal and prismatic. The crystals can
sometimes be twinned, or just come in a crystal cluster.
form is white or
greyish white. It is transculent to almost opaque, and forms crystals
as well as masses, looking exactly like rock crystals in all aspects
except colour. This is actually the most common variety of quartz -
particularly because this is the typre of quartz in the veins.
This variety is most often found as massive, and more seldom as
crystals, even then the crystals are only small. Small amounts of
titanium make it pink.
It is often found in pegmatites,
sometimes in very large amounts. It's the variety of quartz that is
often carved. New Age practitioners also believe that this variety has
a purple, reddish or violet coloured variety of quartz mineral, which
forms crystals and has been a traditional gemstone
since old times. It is widely used in jewelry, either as its natural,
prismatic crystals, or cut gemstones. It is found where granitic rocks
are exposed. Heated amethyst looks like citrine.
Citrine is a
can be any colour between yellow and brown. It is coloured by iron
oxides, but can also be created by heating smoky quartz or amethyst,
which are much more common than citrine. It is often found in
association with the two.
variety is light or
dark brown or any colour in between. The lightest colours can overlap
with rock crystals as there is no exact colour boundary between them.
It is often found in pegmatites. It is relatively abundant and
therefore worth less than some other varieties.
Rutilated quartz. By MAURO CATEB via Flickr.com
formed crystals of rutile in its matrix. Its matrix is most often
transparent while the needles are opaque and if there is a large amount
of needles the whole mineral is opaque. It is most often golden in
colour but can also be reddish. The needles are randomly
Phantom quartz. By jeff-o-matic via Flickr.com
crystals with shadows or "phantoms" from different impurities that have
accumulated in the end of a quartz crystal during its growth. Red and
brown shadows come from iron minerals, white ones from gas, blue from
riebeckite and green from chlorite.
Adventurine. By dee_gee via Flickr.com
Polished on the photo at left, aventurine
is a quartz mineral that is always massive in habit. It has got a
spangled look because of
internal reflections from tiny inclusions from other minerals which are
uniformly oriented. The inclusions can be blue, yellow, orange, white,
red, brown, or green. Red ones come from hematite. Brown ones come from
pyrite. Green ones come from a rare green mica.
Cat's eye quartz. By thisisbossi via Flickr.com
There are two different cat's eye minerals: the less valuable quartz is
called Occidental Cat's
Eye, while the more valuable chrysoberyl is called Oriental Cat's Eye.
Both have a white line across the stone when cut en cabochom style.
That effect comes from parallel asbestos fibres in the quartz.
or Tiger Eye
quartz has a vertical luminescent band called chatoyancy. It is formed
when parallel veins of blue asbestos fibers alter to iron oxides and
later to silica. It has a rich brownish to yellowish colour and is more
opaque than cat's eye. It has got a fibrous habit and vitreous luster.