Gifts
from the Earth:
Where Do Gemstones Come From?
For thousands of years humans have
collected, hoarded, traded, stolen and looted cut and polished stones
of various sorts. By far, the stones most highly prized by cultures
around the world are those we classify as gemstones.
Wars have been waged, and families torn apart by their allure while
the mystique and power we have imbued in these glittering stones have
spawned legends. Unmatched beauty, purity, rarity, and endurance are
the ultimate qualities of the most highly prized gemstones. Join us
as we profile the rarest and most precious of gemstones and explore
the geologic processes that forge them...
Click on any of the images to
see the source and find more fascinating information about these beautiful
gems
Corundum
Al2O3;
Aluminum Oxide
This is not a mineral you often
hear about, but it is the second hardest natural
mineral known to man. Aluminum Oxide, as it is known in mineralogy
circles, is formed by both volcanic processes deep in the earth and
the high pressure and temperature, conditions of metamorphic processes.
As liquid magma deep within the earth slowly cools the minerals dissolved
within cool into crystals. The purest and most translucent forms of
corundum are created by recrystallization of minerals during the metamorphosis
of rocks that are of igneous origin. It is a process that takes millions
of years and only a few places in the world have rock outcrops where
these rare crystals are exposed by weathering.
The pure form of the mineral corundum
is clear and colorless, but mineral 'impurities' that seep into the
Aluminum Oxide as the rock cools give it its fabulous colors. The
distinctive colors of many gemstones are caused by the presence of
transition metals as impurities in an otherwise transparent crystal
lattice. This is a called crystal-field or, a ligand-field effect.
Corundum comes in many different colors, all of which are highly prized
if they are free of intrusions and translucent or transparent. When
trace amounts of titanium and iron get into the Al2O3 crystal lattice
during its formation a beautiful blue sapphire
is formed...more about sapphires->
