Apatite

Description

Apatite is a group of phosphate minerals, typically referring to fluorapatite, chlorapatite, and hydroxylapatite, which are end-members of an isomorphous series. It is the most common phosphate mineral and is ubiquitous in igneous, metamorphic, and sedimentary rocks. Its name comes from the Greek word 'apatein', meaning 'to deceive', due to its resemblance to other minerals like beryl, tourmaline, and olivine. Apatite is the primary mineral in tooth enamel and bone, making it biologically significant.

How to Identify

Color

Highly variable; commonly green, blue, yellow, brown, pink, purple, colorless, or white. Often translucent to transparent.

Luster

Vitreous to sub-resinous.

Texture

Typically crystalline, often forming well-formed hexagonal prisms. Can also be massive, granular, or botryoidal.

Crystal Form

Hexagonal system, typically forming prismatic crystals with pyramidal or pinacoidal terminations. Can also be tabular or acicular.

Cleavage

Poor to indistinct on {0001} and {1010}.

Geological Environment

Found in igneous rocks (e.g., granites, syenites, carbonatites, pegmatites), metamorphic rocks (e.g., marbles, gneisses, schists), and sedimentary rocks (e.g., phosphorites). Also occurs in hydrothermal veins.

Key Facts

• Hardness: 5 (Mohs scale)
• Specific Gravity: 3.1-3.2
• Crystal System: Hexagonal
• Color: Highly variable (green, blue, yellow, brown, pink, purple, colorless, white)
• Luster: Vitreous to sub-resinous
• Transparency: Transparent to translucent
• Fracture: Conchoidal to uneven
• Cleavage: Poor to indistinct on {0001} and {1010}
• Composition: Calcium phosphate with varying amounts of fluoride, chloride, and hydroxyl ions.

Quick Check

• Color: Variable (green, blue, yellow, brown, pink, purple, colorless, white)
• Luster: Vitreous to sub-resinous
• Streak: White

Physical Characteristics

• Crystal Habit: Prismatic, tabular, acicular, massive, granular, botryoidal
• Cleavage Type: Poor to indistinct basal {0001} and prismatic {1010}
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to sub-resinous

Formation

Apatite forms in a wide variety of geological environments. It is a common accessory mineral in igneous rocks (e.g., granites, syenites, carbonatites, pegmatites), metamorphic rocks (e.g., marbles, gneisses, schists), and sedimentary rocks (e.g., phosphorites, limestones, sandstones). It can also form through hydrothermal processes and as a primary precipitate in some sedimentary basins. Biogenic apatite is the primary mineral component of bones and teeth in vertebrates.

Usage

The primary industrial use of apatite is as the main source of phosphorus for fertilizers and phosphoric acid production. It is also used in the production of detergents, pharmaceuticals, and as a gemstone (though relatively soft). Synthetic hydroxylapatite is used in biomedical applications for bone grafts and dental implants due to its biocompatibility.

Age Distribution

Found in rocks of all ages, from Precambrian to Cenozoic, depending on the geological environment.

Where to Find

Finding Tips

Similar Rocks

Scientific Classification

Mineral Class

Phosphates

Group

Apatite Group

Crystal System

Hexagonal

Chemical Formula

Ca5(PO4)3(F,Cl,OH)

Composition

Calcium phosphate with fluoride, chloride, or hydroxyl. End-members are Fluorapatite (Ca5(PO4)3F), Chlorapatite (Ca5(PO4)3Cl), and Hydroxylapatite (Ca5(PO4)3OH).

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