Physical Properties of Citrine for Identification and Classification Purposes
This site contains information on the Physical Properties and Chemical Composition of Minerals, gemstones, crystals, precious metals, and sedimentary, igneous and metamorphic rocks for crystallography, geology, identification of minerals, Jewelry and mineralogy. This includes cleavage, description of crystal formations, crystal structure, hardness, specific gravity, Mohs’ Scale, crystal features and crystal habits for identification and classification purposes.
Citrine is one of the most valuable forms of quartz. The most common use is as a gem by jewelers but is also valuable to mineral collectors. It has also substituted for the more expensive gem Topaz.
Color
Citrine is transparent to translucent and yellow to gold-brown in color
with a vitreous luster. The name citrine is derived from the old French
word for lemon, citrin. Its color comes from the presence of Iron
impurities within the crystal. The darker colored Citrine crystals, named
Madeira for their color’s resemblance to Madeira wines, are generally
more valuable. Natural citrine is rare and most natural occurs when
Amethyst formations are near natural heat sources in the Earth’s crust.
Citrine becomes dark brown when exposed to x-rays and white when heated.
Shape
Citrine crystals occur in nature
in protruding clusters of pyramids on a geode base. They are Trigonal, a
less symmetrical subset of the Hexagonal (six sides) system with four
crystallographic axes, three in the same plane intersecting at 60 degree
angles and the fourth, shorter or longer axis, intersecting the plane of
the other three at an angle of 90 degrees. The typical cutting styles for
Citrine include, faceted, cabochons, beads and carvings.
Heated
Amethyst
As mentioned above, Citrine deposits are rare. In fact, most Citrine
sold is actually inexpensive pieces of smoky Quartz or Amethyst heated by
jewelers to 878 degrees or higher to attain the stone’s yellow color.
Red tints on the heated Amethyst distinguish it from genuine Citrine,
which is generally pale yellow.
Fake
Topaz
Because Citrine closely resembles the more expensive stone Topaz in color,
many jewelers sell it as Topaz. Some have chosen false names for Citrine
when representing it as Topaz, such as Gold Topaz, Madeira Topaz,
Brazilian Topaz and Citrine Topaz. These are merely heat-treated Topaz.
This form of unscrupulous behavior is unfortunately the source of some
negativity toward Citrine, which is sad because most gemologists consider
Citrine a fine stone in its own right. To distinguish Citrine from Topaz,
consider Topaz’ hardness of 8, which is higher than Citrine’s hardness
of 7 and that Topaz crystals have perfect cleavage.
Ametrine
Because heated Amethyst becomes Citrine, whether through natural or
synthetic processes, and the processes are not always uniform, mixing of
Amethyst’ purple color and Citrine’s yellow can occur. This results in
Ametrine. Natural occurrences come from the Anahi mine in Bolivia.
CHEMICAL
COMPOSITION
SiO2 with colloidal iron hydrates. Citrine is a member of the
silicate, tectosilicate, silica groups. Gemologists also classify
Citrine as an oxide. Citrines are
tough stones and may be cleaned with jewelry cleaners, soap, or an
untreated cloth.
Hardness:
7
Specific Gravity:
2.6 - 2.7
Cleavage:
none
Fracture:
conchoidal, very brittle
Refractive Index:
1.544
Birefringence:
0.009
Cleavage:
Indiscernible
Fracture:
Conchoidal
Tenacity:
Brittle
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