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
Monoclinic – The monoclinic system has a minimum symmetry of the one two-fold axis.
Cubic or Isometric – Crystals in the cubic system have the highest symmetry. The minumum symmetry is four-fold axes.
Tetragonal – This system is defined by one four-fold axis.
Orthorhombic – The minimum symmetry of this system is three two-fold axis.
Triclinic – Crystals of this system have no axis of symmetry, so gemstones within this system are the least symmetrical.
|
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 |
