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Apatite
is actually three different minerals depending on the predominance
of either fluorine, chlorine or the hydroxyl group. These ions can
freely substitute in the crystal lattice and all three are usually
present in every specimen although some specimens have been close
to 100% in one or the other. The rather non-inventive names of these
minerals are Fluorapatite, Chlorapatite and Hydroxylapatite. The
three are usually considered together due to the difficulty in distinguishing
them in hand samples using ordinary methods.
An
irony of the name apatite is that apatite is the mineral that makes
up the teeth in all vertebrate animals as well as their bones. Get
it? Apatite - teeth! Anyway, the name apatite comes from a Greek
word meaning to decieve in allusion to its similarity to other more
valuable minerals such as olivine, peridot and beryl.
Apatite
is widely distributed in all rock types; igneous, sedimentary and
metamorphic, but is usually just small disseminated grains or cryptocrystalline
fragments. Large well formed crystals though can be found in certain
contact metamorphic rocks. Very gemmy crystals of apatite can be
cut as gems but the softness of apatite prevents wide distribution
or acceptance of apatite as a gemstone.
PHYSICAL CHARACTERISTICS:
Color is typically green but also yellow, blue, reddish brown and purple.
Luster is vitreous to greasy and gumdrop.
Transparency: Crystals are transparent to translucent.
Crystal System is hexagonal; 6/m
Crystal Habits include the typical hexagonal prism with the hexagonal
pyramid or a pinacoid or both as a termination. Also accicular, granular,
reniform and massive. A cryptocrystalline variety is called collophane
and can make up a rock type called phosphorite and also can replace
fossil fragments.
Cleavage is indistinct in one basal direction.
Fracture is conchoidal.
Hardness is 5.
Specific Gravity is approximately 3.1 - 3.2 (average for translucent
minerals)
Streak is white.
Associated Minerals are hornblende, micas, nepheline and calcite.
Other Characteristics: An unusual "partially dissolved" look
similar to the look of previously sucked on hard candy.
Notable Occurrences include Durango, Mexico; Bancroft, Ontario; Germany
and Russia.
Best Field Indicators are crystal habit, color, hardness and look.
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