QUARTZ
...
is the second most common
mineral in the Earth's continental crust.
It is made up
of a lattice of silica. Quartz goes by an array of
different names.
The most important distinction between
types of quartz is either where individual crystals are
visible to the unaided eye or the Chalcedony varieties
where crystals are visible only under high
magnification. Not all varieties of quartz are naturally
occurring. Prasiolite, an olive coloured material, is
produced by heat treatment. Although citrine occurs
naturally, most is the result of heat-treated amethyst.
Carnelian is widely heat-treated to deepen colour.
Major
varieties include:
|
Chalcedony |
Any
fine crystaline quartz but only used for white
or lightly coloured |
|
Agate |
Multi-coloured,
banded Chalcedony, semi-translucent to
translucent |
|
Onyx |
Agate
where the bands are straight, parallel and
consistent in size. |
|
Jasper |
Opaque
chalcedony, impure |
|
Adventurine |
Translucent
chalcedony with small inclusions that shimmer
(mica) |
|
Tiger
eye |
Fibrous
gold to red-brown coloured quartz, exhibiting
optical reflection |
|
Amethyst |
Purple,
transparent |
|
Citrine |
Yellow
to reddish orange to brown, greenish yellow |
|
Prasiolite |
Mint
green, transparent |
|
Rose
quartz |
Pink,
translucent, may display a reflected star |
|
Milk
quartz |
White,
translucent to opaque |
|
Smoky
quartz |
Brown
to grey, opaque |
|
Carnelian |
Reddish
orange chalcedony, translucent |
|
|
|
