|
|
|
| Quartz |
| GEOBITS
of Jade: |
 |
How many varieties of quartz do you
know? Quartz, a silica and the most common mineral,
can occur in many forms. It can be ultra-fine grained (cryptocrystalline)
or appears with an extraordinary colour when it contains
certain elements or impurities. The charts below are
some of the most common varieties of quartz. Some high-pressure
forms of quartz such as coesite and stishovite are rare
in nature and high-temperature forms such as tridymite
and cristobalite can be identified only with a microscope. |
|
Varieties
of Cryptocrystalline Quartz
Note:
Chalcedony (pronounced kal-sed?o-nee) is the
name for cryptocrystalline quartz. The following are
names for varieties of chalcedony known through the
centuries. This list is by no means authoritative; no
list can be, as there is much confusion, disagreement,
and misunderstanding over these varieties and their
names.
|
|
Variety Name
|
Color
|
Causes
of Color
|
|
Chalcedony
(Catch-all
for colors
not described by one
of following varieties)
|
Pale gray, blue-gray, blue,
black,
brown, colorless
|
Impurities
|
|
Agate
|
Distinctly
banded chalcedony with
successive layers differing in color
or with distinctive patterning
|
-
|
|
Onyx
|
Banded agate with layers
of
contrasting color in parallel straight
lines
|
-
|
|
Carnelian
|
Translucent blood red to brownish-
Red
|
Iron
|
|
Sard (also called
sardius)
|
Translucent light brown to
yellowish
brown to dark brown
|
Iron
|
|
Sardonyx
|
Translucent
red or brown layers
with white layers
|
-
|
|
Moss Agate
|
Gray, bluish or milky transparent to
translucent
chalcedony enclosing
moss-like
crystal growths
|
Manganese oxide, chlorite,
goethite,
hematite, and others
|
|
Chrysoprase
|
Translucent apple green
|
Colloidal nickel compound
|
|
Plasma
|
Opaque leek green to dark
green
|
Green silicate minerals
|
|
Prase
|
Translucent
leek green
|
Chlorite, pyroxene, or
amphibole
inclusions
|
|
Bloodstone (or
Heliotrope)
|
Plasma with red spots
|
Hematite
or red jasper
|
|
Jasper
|
Opaque shades of red, brown,
|
Iron
oxides, other compounds
|
|
Chert
|
Opaque white to light gray
|
-
|
|
Flint
|
Dark gray to black
|
-
|
|
|
| Varieties
of Crystalline Quartz |
|
Variety Name
|
Colors
|
Causes of Color
|
|
Rock Crystal
|
Colorless, transparent
|
Iron plus irradiation
|
|
Amethyst
|
Various shades of purple
or violet
|
-
|
|
Citrine
|
Various shades of yellow,
yellow-brown, yellow-orange
|
Iron impurities; most
citrine is made by heating amethyst
|
|
Smoky Quartz (also called Cairngorm, or if black, Morion)
|
Pale smoky brown to almost black;
can be opaque
|
Aluminum impurities plus irradiation
|
|
Rose Quartz
|
Pale pink to deep red rose;
sometimes shows asterism (star)
|
Titanium
|
|
Blue Quartz
|
Pale blue, grayish blue to lavender
blue; rare; somewhat chatoyant
|
Scattering of light by tiny needles of rutile or other crystals
|
|
Green Quartz (Praziolite)
|
Green
|
Iron, heat
|
|
Milky Quartz
|
Milky white to grayish white;
can be nearly opaque
|
Numerous gas and liquid inclusions
|
|
| Quartz
Varieties with Inclusions |
|
Rutilated Quartz
(also catseye, when chatoyant;
sagenite, when a netlike pattern)
|
Colorless to yellow, red or
brownish acicular (hairlike)
crystals included in quartz crystal
|
Contains distinct acicular rutile crystals in
sprays or random orientation
|
|
Tourmalinated Quartz
|
Black colored acicular (hairlike)
fibers inclusions
|
Contains distinct acicular
tourmaline crystals
|
|
Aventurine
|
Green, brick red
|
Green caused by spangling of
minute mica crystals; red, by
hematite
|
|
Tigereye
(also hawkseye, with blue
chatoyancy from blue asbestos)
|
Fibrous yellow, yellow-brown,
brown, reddish brown, bluish,
grayish-green, green, chatoyant
|
Formed by replacement of asbestos
|
|
|
| This
issue of Geobits was contributed by Dr. L.S. CHAN |
| |
|
Thank
you for your visit. |
|
|
