Apatite
Structure : Hexagonal
Hardness : 5
Specific Gravity : 3.2
Refractive index : 1.63- 1.64
Doubly Refracting (bi-refraction) : 0.003
Chemistry: Ca5(PO4)3(OH,F,Cl), Calcium (Fluoro, Chloro, Hydroxyl) Phosphate
Class: Phosphates
Group: Apatite
Uses: as a source of phosphorous to be used in fertilizer, rarely as a
gemstone and as a mineral specimen.
Specimens
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.
