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Colour of Stone Beads
Colour can be a useful clue to aid in identification of a gem, but
it can also mislead, so beware! Gemstone may look different under
different light sources; for example, CHRYSOBERYL with a colour change
may show flashes of green in daylight, but has flashes of red indoors
under artificial light. The colour of a gemstone may be enhanced or
altered , and imitations may be fashioned to look exactly the same
colour as the natural gem they imitate.
A gemmologist will take the colour of the gemstone into account, but
will also look for other clues; for example, wear and tear of the
facet edges, scratches and pit marks give an idea of hardness, while
fire and sparkle suggest possible values for dispersion and refractive
index. Appropriate tests may then need to be carried out to establish
the identification of the gemstone.
The major ore of tin, cassiterite is also appreciated for its sparkle,
derives from its high lustre. It is found as an eight-sided pri consisting
of two four-side prisms, one of which is usual dominant. While it
is generally black, reddish-brown crystals, large enough for cutting,
are also occasionally found. It is named from the Greek word kassiteros
for tin.
Cassiterite's importance as tin ore has been known for millennia.
During the Bronze Age, it was added to molten copper to form bronze,
a copper alloy that is strong and durable yet easily worked. Some
of the oldest cassiterite mines, such as those in Cornwall, England,
have been worked since 2000 Bc and are now exhausted of minerals.
Cassiterite is generally located within or near granite masses. It
is associated with wolframite, arsenopyrite, bismuthinite, TOPAZ,
QUARTZ, TOURMALINE, and mica. Today, because so many established mines
have been intensively worked over the centuries, most cassiterite
is found in alluvial deposits.
In addition to its industrial use as a source of tin, cassiterite
is also used as a gemstone. it needs polishing to bring out its best,
which may be time-consuming, but cutting is straightforward because
it is hard and cleavage is imperfect. Large cut stones, of more than
one carat, are rare. The best stones for cutting come from Erongo,
central Namibia, and from Galicia, stone bead wholesale Spain.
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