Chemistry: |
SiO2 , Silicon dioxide |
Class: |
Silicates |
Subclass: |
Tectosilicates |
Group: |
Quartz |
Uses: |
silica for glass, electrical components, optical lenses,
abrasives, gemstones, ornamental stone, building stone,
etc. |
Color: |
variable as the spectrum, but clear quartz is by far
the most common color followed by white or cloudy (milky
quartz). Purple (Amethyst), pink (Rose Quartz), gray
or brown to black (Smoky Quartz) are also common. Cryptocrystalline
varieties can be multicolored. |
Luster: |
glassy to vitreous as crystals, while cryptocrystalline
forms are usually waxy to dull but can be vitreous. |
Transparency: |
crystals are transparent to translucent, cryptocrystalline
forms can be transparent, translucent or opaque. |
Crystal System: |
trigonal; 32 |
Crystal Habits: |
are again widely variable but the most common habit
is hexagonal prisms terminated with a six sided pyramid
(actually two rhombohedrons). Three of the six sides
of the pyramid may dominate causing the pyramid to be
or look three sided. Left and right handed crystals
are possible and identifiable only if minor trigonal
pyramidal faces are present. Druse forms (crystal lined
rock with just the pyramids showing) are also common.
Massive forms can be just about any type but common
forms include botryoidal, globular, stalactitic, crusts
of agate such as lining the interior of a geode and
many many more. |
Cleavage: |
not present |
Fracture: |
conchoida |
Hardness: |
7, less in cryptocrystalline form |
Specific Gravity: |
2.65 or less if cryptocrystalline. (average) |
Streak |
white. |
Other Characteristics: |
striations on prism faces run perpendicular to C axis,
piezoelectric (see tourmaline) and index of refraction
is 1.55. |
Associated Minerals: |
are numerous and varied but here are some of the more
classic associations of quartz (although any list of
associated minerals of quartz is only a partial list):
amazonite a variety of microcline, tourmalines especially
elbaite, wolframite, pyrite, rutile, zeolites, fluorite,
calcite, gold, muscovite, topaz, beryl, hematite and
spodumene. |
Local Occurance: |
Desmont Mine, MacDonald Mine, Musclow Occurrence, Quirk
Lake Occurrenceamethyst - purple variety of quartz.
- Musclow Occurrencesmoky - brown to black variety of
quartz; - Musclow Occurrence, Beryl Pit |
Best Field Indicators: |
are first the fact that it is very common (always
assume transparent clear crystals may be quartz), crystal
habit, hardness, striations, lack of cleavage and good
conchoidal fracture. |
Description:
Additional variety specimens include: Amethyst
Citrine
Rock Crystal
Rose Quartz
Smoky Quartz Quartz is the most common mineral on the
face of the Earth. It is found in nearly every geological
environment and is at least a component of almost every
rock type. It frequently is the primary mineral, >98%.
It is also the most varied in terms of varieties, colors
and forms. This variety comes about because of the abundance
and widespread distribution of quartz. A collector could
easily have hundreds of quartz specimens and not have
two that are the same due to the many broad catagories.
The specimens could be separated by answers to the following
questions: color?, shade?, pyramidal?, prismatic?, druzy?,
twinned?, sceptered?, tapered?, phantomed?, inclusions?,
coated?, microcrystalline?, stalactitic?, concretionary?,
geoidal?, tappered?, banded?, etc. Multiple combinations
of these could produce hundreds of unique possibilities.
Some macrocrystalline (large crystal) varieties are
well known and popular as ornamental stone and as gemstones. Amethyst is the purple gemstone variety. Citrine is a yellow to orange gemstone variety that is rare
in nature but is often created by heating Amethyst. Milky Quartz is the cloudy white variety. Rock
crystal is the clear variety that is also used as
a gemstone. Rose quartz is a pink to reddish
pink variety. Smoky quartz is the brown to gray
variety. Cryptocrystalline (crystals too small to be
seen even by a microscope) varieties are also used as
semi-precious stones and for ornamental purposes. These
varieties are divided more by character than by color.
Chalcedony or agate is divided into innumeral types
that have been named for locally common varieties. Some
of the more beautiful types have retained their names
on a world-wide basis while other names have faded into
obscurity. Some of the more common of these types are
chrysoprase (a pure green agate), sard (a yellow to
brown agate), sardonyx (banded sard), onyx (black and
white agate), carnelian (a yellow to orange agate),
flint (a colorful and microscopically fibrous form),
jasper (a colorful impure agate) and bloodstone (a green
with red speckled agate). Quartz is not the only mineral
composed of SiO2. There are no less than eight other
known structures that are composed of SiO2. These other
substances and quartz are polymorphs of silicon dioxide
and belong to an informal group called the Quartz Group
or Silica Group. All members of this group, except quartz,
are uncommon to extemely rare on the surface of the
earth and are stable only under high temperatures and
high pressures or both. These minerals have their own
unique structures although they share the same chemistry,
hence the term polymorph, which means many forms. Quartz
has a unique structure. Actually, there is another mineral
that shares quartz's structure, and it is not even a
silicate. It is a rare phosphate named berlinite, AlPO4,
that is isostructural with quartz. The structure of
quartz involves corkscrewing (helix) chains of silicon
tetrahedrons. The corkscrew takes four tetrahedrons
in order to repeat itself, or three turns. Each tetrahedron
is essentially rotated 120 degrees. The chains are aligned
along the c axis of the crystal and interconnected to
two other chains at each tetrahedron making quartz a
true tectosilicate. This structure is not like the structure
of the chain silicates or inosilicates whose silicate
tetrahedronal chains are not directly connected to each
other. The structure of quartz helps explain many of
its physical attributes. For one, the helix makes three
turns and this helps produce the trigonal symmetry of
quartz. Likewise a helix or corkscrew lacks mirror planes
of symmetry as does quartz. The corkscrew structure
would also disrupt any cleavage which requires a plane
of weakness not found in quartz and breakage would result
in the curved fracture, conchoidal, that is found in
quartz. Quartz can also have left and right handed crystals
just as a corkscrew can screw in a left handed way or
in a right handed way. There are even some very difficult
to identify crystals of quartz that are twinned with
alternating one sixths of the crystal being right handed
and then left handed. Quartz is a fun mineral to collect.
Its abundance on the Earth's surface is incredible and
produces some wonderful varieties that don't even look
like the same mineral. A collector must always be up
on the many varieties of quartz and it sometimes embarrasses
a collector to have collected too many specimens of
such a common mineral. But nearly all collectors concede
that you can never really have enough quartz specimens. |
|