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CRYSTAL SYSTEMS
Although traditionally crystal systems are not part of the physical
properties table of gemstones, but most mineral gemstones are crystaline,
with thier atoms arranged in regular and symmetrical patterns. Crystal
systems are classifed into seven different systems, according to the
"minimum symmetry" of their faces.
-
Hexagonal/Trigonal – This
systems share the same axis of symmetry
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Monoclinic – The monoclinic
system has a minimum symmetry of the one two-fold axis.
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Cubic or Isometric – Crystals
in the cubic system have the highest symmetry. The minumum symmetry is
four-fold axes.
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Tetragonal – This system is
defined by one four-fold axis.
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Orthorhombic – The minimum
symmetry of this system is three two-fold axis.
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Triclinic – Crystals of this
system have no axis of symmetry, so gemstones within this system are the
least symmetrical.
IMPORTANT PROPERTIES OF A FEW GEMSTONES
|
Name |
Hardness |
Chemical Formula |
Density |
Crystal |
|
Agate |
6.5 - 7 |
SiO2 |
2.57 - 2.64 |
Hexagonal |
|
Alexandrite |
8.50 |
BeAl2O4 |
3.73 |
Orthorhombic |
|
Amethyst |
7 |
SiO2 |
2.66 |
Hexagonal |
|
Aquamarine |
7.5 |
Be3Al2(SiO3)6 |
2.67-2.745 |
Hexagonal |
|
Calcite |
3 |
CaCO3 |
2.70 |
Triclinic |
|
Cats Eye |
8.5 |
BeAl2O4 |
3.73 |
Orthorhombic |
|
Diamond |
10 |
C |
3.52 |
Cubic |
|
Emerald |
7.5-8 |
Be3Al2(SiO3)6 |
2.72 (-.05, +.12) |
Hexagonal |
|
Fluorite |
4 |
CaF2 |
3.18 |
Cubic |
|
Fresh Water Pearls |
3.5 - 4.0 |
CaCO3 |
2.66 – 2.78+ |
Not applicable |
|
Jadeite |
7 |
NaAl(SiO3)2</SUB<
SPAN> |
3.32 |
Monoclinic |
|
Mali Garnet |
7.25 |
Ca3Al2(SiO4)3 |
3.65 |
Cubic |
|
Moonstone |
6 – 6.50 |
KalSI3O8 |
2.55 – 2.57 |
Monoclinic |
|
Opal |
5.5 - 6.0 |
SIO2nH2O |
2.65 - 3.00 |
Amorphous |
|
Peridot |
6.5 |
(Mg,Fe)2(SiO)4 |
3.34 |
Orthorhombic |
|
Quartz |
7 |
SiO2 |
2.65 |
Trigonal |
|
Ruby |
9 |
AL2O3 |
4.00 |
Hexagonal |
|
Sapphire |
9 |
AL22O3 |
4.00 |
Hexagonal |
|
Spinel |
8 |
MgAl2O4 |
3.60 (-.03, +.30) |
Cubic |
|
Star Sapphire |
9 |
AL2O3 |
4.00 |
Hexagonal |
|
Tanzanite |
6-7 |
Ca2(Al,OH)Al2(SIO4) |
3.30 (+.10, -.10) |
Orthorhombic |
|
Topaz |
8 |
AL(F,OH)2SIO4 |
3.52 - 3.56 |
Orthorhombic |
|
Turquoise |
5.5-6 |
CuAl6(PO4)4(OH)85H2O |
2.60- 2.90 |
Triclinic |
Natural Gemstones |
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