There's a small pun in this category name; obviously, quartz is a rock but the category name
refers to my enthusiasm with the beautiful variety by this most awesome gemstone. The base chemical
structure is always the same (SiO2): silica tetrahedra with shared corners, increasing the silicon to oxygen
ratio to 1:2 instead of 1:3 or 1:4. There's the
"macrocrystalline" quartz in which individual crystals are visible to the naked eye (think clusters
of prismatic crystals in a geode); examples include amethyst, citrine, rose quartz and smoky quartz.
"Microcrystalline" quartz show individual crystals under magnification and tend to be
more translucent to opaque; examples include agate, carnelian, chalcedony and jasper. Quartz is the second
most abundant mineral in the Earth's crust, after feldspar, so it is found everywhere. Trace amounts of elements
like titanium (rose quartz), iron oxide (citrine and amethyst), hematite (red jasper) and nickel (chrysoprase)
give the stones their color.
For colorful stones like banded agate, jasper and sardonyx, the colors form as a result of slight element changes
during the deposition of the silica.
•• a g a t e
Agate is a type of chalcedony that is characterized by various patterns. Most agate
is banded in concentric forms, but it can also form with dendrite-like inclusions
(moss agate). Banded agate may be simple, as in Brazilian agate with concentric
circles, or convoluted like the "crazy lace" agate found in Mexico. Blue-lace
agate from South Africa is pale blue with delicate layers of lighter and darker hues.
Fire agate includes red to brown hematite which goes the stones inner iridescence. A common
place to find moss agate is Medford, Oregon. The Petrified Forest in Arizona is agatized
wood in which the organic matter has been replaced by agate. Agate is often dyed in
vibrant colors that highlight patterns in the stone.
•• a m e t h y s t
Amethyst has long been associated with royalty and purity; deep purple stones tend
to be the most valuable, but lavender amethyst can also be lovely. The name comes from
Greek for "not drunk", referring to the myth in which Dionysus created amethyst
in repentance for sending tigers to devour a young maid. It was thought that drinking from
amethyst cups would protect the drinker from drunkenness. On the opposite end of the spectrum,
the early Christian church adopted amethyst as a symbol of purity, and amethyst rings were
given to bishops. Amethyst is also reportedly one of the original stones of the twelve tribes
of Israel on Aaron's breastplate. Brazil is the best known source for amethyst, but deposits are
also found in Siberia and North America. The characteristic purple color is due to traces of
iron, and amethyst can be heat-treated to create citrine.
•• a m e t r i n e
As the name suggests, ametrine is a stone with naturally occurring amethyst and
citrine. Both amethyst and citrine are varieties of quartz colored by iron or
iron oxide, so the transition between amethyst and citrine can be a subtle one
leading to beautiful stones.
•• a v e n t u r i n e
Aventurine is a type of quartz spotted or spangled in appearance due to inclusions
of hematite (red aventurine), green fuchsite mica (green aventurine) or other
minerals. When these inclusions are uniformly distributed and oriented, aventurine
shows nice sparkle from the internal reflections. It's always found in massive form
and has no cleavage planes so it's often used in cabachons.
•• c a r n e l i a n
Iron oxide is responsible for the deep red-orange color of carnelian, a variety of
chalcedony. It can be banded like agate or uniform in color and it can be light
orange to deep blood-red in color. Like amethyst, it has a long history, used by
Egyptians, Greeks and Romans, and it's also thought to be one of the twelve gemstones
on Aaron's breastplate. India produces fine quality carnelian, as well as Scotland,
Brazil and Washington. Natural carnelian is rare and therefore quite expensive, so most
jewelry components are actually
agate that has been heat treated and/or dyed.
•• c h a l c e d o n y
Chalcedony is a compact microcrystalline quartz that forms in cavities and cracks
as silica-rich waters percolate through existing structures. Naturally it's pale in
color but relatively porous, which works well for dyes. Most chalcedony jewelry components
are dyed and subject to fading with time and exposure to sun.
•• c h a m p a g n e q u a r t z
Champagne quartz is a pale, smooth, golden colored stone. It is a macrocrystalline quartz found in
similar areas to crystal quartz and smoky quartz.
•• c h r y s o p r a s e
Chrysoprase is a variety of chalcedony (microcrystalline quartz) with distinctive
apple-green to blue-green color from trace amounts of nickel. It is the most valuable
of the chalcedonies and most fine quality stones come from Queensland, Australia. The Ural
mountains in Russia, Brazil and California are other sources. It is generally untreated and
the color may fade with exposure to sun.
•• c i t r i n e
Citrine is a yellow to yellow-orange color of macrocrystalline quartz. Hydrous iron
oxide is responsible for the color, and many citrine components on the market are
actually heated amethyst, which has similar composition. Transitions between
amethyst and citrine occur naturally and stones showing this are called ametrine.
Citrine is commonly heated to enhance color and sometimes dyed as well. High quality
stones come from Scotland, Russia, France, Brazil and North Carolina.
•• c r y s t a l q u a r t z
Crystal quartz or rock crystal is a colorless variety of macrocrystalline quartz. Quartz occurs
in all kinds of silica-rich rocks (metamorphic, sedimentary, igneous) so the mineral itself is
common, though finding flawless icelike specimens is not. It has been carved and used since ancient
times; the name "quartz" is from Old German and crystal is derived from the Greek
•• g r e e n q u a r t z
Green quartz or prasolite is sometimes sold as green amethyst, which is a misnomer since by definition,
amethyst is purple quartz. However, it is fair to say that green quartz comes from amethyst.
When natural amethyst is heated - either in a lab or by proximity to molten lava - it can
produce prasiolite (green quartz). Prasiolite can also be created through radiation, though
the color of irradiated green quartz tends to be less stable than heated green quartz. Green
quartz is a pale fern or forest green and transparent, like the parent amethyst.
•• j a s p e r
Jasper is an opaque microcrystalline quartz that forms via deposition from
silica-rich waters, like agate and other chalcedonies. There are numerous types
of jasper, such as moukaite jasper from Australia, colored with clay and iron
oxide, picasso jasper from Utah with striking patterns of black with gray,
brecciated jasper that's a deep brick red from iron oxides and organic material,
autumn jasper with swirls of red-brown and green, and fancy jasper that is a mix of
muted jewel-tone hues.
•• o n y x
Althought most onyx jewelry components are solid black, the definition of onyx is
a striped variety of agate with white and black alternating bands. In fact, most
"onyx" is agate that has been dyed black since uniform deep black is unusual
to find in a mineral, other than schorl (black tourmaline) or jet. India and South
America are the primary sources of natural onyx.
•• q u a r t z
This is a general category of quartz stones such as snow quartz, milky quartz or fossilized silicates
like ammonites or petrified wood that don't fall into a different category.
•• r o s e q u a r t z
Rose quartz is a translucent or transparent pink crystalline quartz. It is more commonly
found in aggregate rather than prismatic form, and it may be transparent or cloudy due to
minute rutile inclusions. Like amethyst and other macrocrystalline quartz, it is found
in pegmatites. The primary sources are Madagascar, Brazil, Namibia, Sweden, Russia, Spain
and the US states of California and Maine. It is often dyed to enhance or deepen the pink
•• r u t i l a t e d q u a r t z
Rutile is a form of titanium oxide and rutilated quartz a variety of quartz that includes
needle-like rutile within it. The quartz is typically transparent with various density of
rutile needles; there may be few to so dense that the stone appears opaque in areas. The
rutile is typically golden in color but can also be deep red to black. Black tourmaline
may behave like rutile and show black needle-like inclusions; this is called
tourmalated quartz and may be difficult to distinguish from rutilated quartz.
•• s a r d o n y x
Sardonyx is onyx (variety of striped agate) though with the red-orange sard mineral
instead of dark brown or black of onyx. Sard is similar to carnelian, though it tends to be
slightly harder and darker red to red-brown.
•• s m o k y q u a r t z
Smoky quartz is the brown color variety of macrocrystalline quartz whose color, like
amethyst, is caused by the interaction of radiation with aluminum impurities within
the crystalline structure. Smoky quartz is abundant, and it is possible to find jewelry
components of excellent color and clarity at relatively inexpensive cost. Smoky quartz
may be heated or irradiated to improve the color from grey-brown to a rich mocha color
that is more popular.
•• t i g e r s e y e
Tiger's eye quartz is formed when parallel veins of crocidolite (blue asbestos) fibers
are first altered to iron oxides then covered by silica. This leads to chatoyancy,
a luminescent band appearing across the stone. The iron oxide gives tiger's eye a rich
yellow to brown color. Blue tiger's eye is a natural stone in which silica covers the
crocidolite directly, maintaining the blue-grey color. It should be noted that the asbestos
fibers in the stones area altered or covered by other materials, so there is no risk of
exposure. Tiger's eye comes from South Africa and Queensland, Australia.