Thursday, September 10, 2009

Apatite / Apatita var. Esparriguina, what a name uh?

This is a beautiful mineral rarely found in good crystals, this particular one from the Market Hill (Cerro del Mercado) in Durango, state of Durango, Mexico. Variety of this pale yellow specimen is named "Esparriguina."

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.

Let's go technical:
Chemical Formula: Ca5(PO4)3(OH,F,Cl)
Name Origin: Named in 1788 from the Greek apatao - "I am misleading." Reason is that it mislead to confuse for some valuable minerals, such as olivinite, etc.
Crystal System: Hexagonal - Dipyramidal
Cleavage: {0001} Indistinct, {1010} Indistinct
Color: White, Yellow, Green, Red, Blue.
Density: 3.16 - 3.22, Average = 3.19
Diaphaneity: Transparent to translucent
Fracture: Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Habit: Colloform - Forming from a gel or colloidal mass.
Habit: Earthy - Dull, clay-like texture with no visible crystalline affinities, (e.g. howlite).
Habit: Massive - Granular - Common texture observed in granite and other igneous rock. 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.
Hardness: 5
Luminescence: Non-fluorescent.
Luster: Vitreous (Glassy)
Streak: 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.
Radioactivity: Apatite is Not Radioactive

I apologize, took a little while to post another one, been busy. I hope you are doing good.

Best regards,
Oscar G. Shelly

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