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Blue Apatite is a calcium phosphate mineral belonging to the apatite group, specifically the fluorapatite end-member. Its distinctive blue color can range from a pale sky blue to a deep, vibrant indigo, often exhibiting pleochroism. It typically forms hexagonal crystals, which can be prismatic or tabular. While relatively soft, its attractive color and clarity make it a popular choice for collectors and in certain jewelry applications. It is an important mineral both geologically and economically.
How to Identify
- Color
- Ranges from pale sky blue to deep indigo blue, sometimes with greenish or violet tints. Often exhibits pleochroism, showing different colors when viewed from different angles.
- Luster
- Vitreous (glassy) to sub-resinous.
- Texture
- Smooth to slightly uneven fracture surfaces.
- Crystal Form
- Typically forms hexagonal prisms, often with pyramidal terminations. Can also be found as tabular crystals, massive, or granular aggregates.
- Cleavage
- Poor to indistinct on {0001} and {1010}.
- Geological Environment
- Found in igneous rocks (especially pegmatites and carbonatites), metamorphic rocks (marbles, gneisses, schists), and hydrothermal veins. Also occurs in sedimentary phosphorite deposits.
Key Facts
- Hardness: 5 on the Mohs scale
- Specific Gravity: 3.16 - 3.22
- Crystal System: Hexagonal
- Color: Blue, often with greenish or violet tints; pleochroic
- 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 fluorine (Ca5(PO4)3F)
Quick Check
- Color: Blue (various shades)
- Luster: Vitreous to sub-resinous
- Streak: White
Physical Characteristics
- Crystal Habit: Hexagonal prismatic, tabular, massive, granular
- 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 range of geological environments. It is a common accessory mineral in igneous rocks (e.g., granites, syenites, carbonatites), metamorphic rocks (e.g., gneisses, schists, marbles), and sedimentary rocks (e.g., phosphorites, shales). Blue apatite specifically often forms in pegmatites, hydrothermal veins, and contact metamorphic zones, where the presence of certain trace elements (like rare earth elements or manganese) can contribute to its blue coloration.
Usage
Blue apatite is primarily used as a gemstone, though its relative softness (Mohs 5) limits its use in jewelry to pieces not subjected to hard wear. It is also a collector's mineral. More broadly, apatite is the primary source of phosphorus for fertilizers and phosphoric acid. It is also used in the production of certain ceramics and as a pigment.
Age Distribution
Apatite minerals are found in rocks of all ages, from Precambrian to Cenozoic, reflecting their widespread occurrence in various geological settings.
Where to Find
Brazil
Minas Gerais is a significant source of gem-quality blue apatite, often found in pegmatites.
Madagascar
Known for producing vibrant blue apatite crystals, particularly from the region of Ambatofinandrahana.
Mexico
Various localities, including Cerro de Mercado, Durango, have produced blue apatite.
Canada
Ontario and Quebec have occurrences of blue apatite, often associated with metamorphic and igneous rocks.
Myanmar (Burma)
Some gem-quality blue apatite has been found in Myanmar.
United States
Localities in Maine, California, and other states have produced blue apatite, though often not gem quality.
Finding Tips
Geological Context
Focus your search in areas known for pegmatites, hydrothermal veins, or contact metamorphic zones, as these are common environments for blue apatite formation.
Associated Minerals
Look for blue apatite alongside minerals commonly found in these environments, such as quartz, feldspar, mica, tourmaline, and other phosphate minerals.
Crystal Habit
Keep an eye out for hexagonal prismatic crystals, which are characteristic of apatite. Even small fragments might show this habit.
Hardness Test (Caution)
Apatite has a Mohs hardness of 5. While not recommended for valuable specimens, a careful scratch test against a known mineral of similar hardness (e.g., fluorite, Mohs 4; orthoclase, Mohs 6) can help differentiate it. Apatite will scratch fluorite but be scratched by orthoclase.
Pleochroism
If you find a transparent blue crystal, rotate it to observe if its color changes when viewed from different angles. This pleochroic effect is common in blue apatite.
Similar Rocks
Blue Topaz
Topaz
Also known as: Aluminum Silicate Fluoride Hydroxide
Aquamarine
Beryl
Also known as: Beryl (blue variety)
Kyanite
Kyanite
Also known as: Disthene
Scientific Classification
- Mineral Class
- Phosphates
- Group
- Apatite Group
- Crystal System
- Hexagonal
- Chemical Formula
- Ca5(PO4)3F
- Composition
- Calcium Fluorophosphate
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