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Entry № 200

Garnet in Biotite

Almandine in Biotite Schist

Metamorphic proof that pressure produces jewels.

Chakra

Root · Solar Plexus

Element

Fire · Earth

Zodiac

Aries · Capricorn

Garnet in Biotite

I. The Metaphysical Reading

How the stone has been held.

Garnet in biotite is worked with as a stone of endured work, carried through training, apprenticeships and slow projects. Practitioners hold that the biotite records the layered effort while the garnet marks the moments where that effort became structure.

Chakra
Root · Solar Plexus
Element
Fire · Earth
Zodiac
Aries · Capricorn
Keynote
Metamorphic proof that pressure produces jewels.

II. The Scientific Reading

What the lattice actually does.

Garnet-biotite schist is one of the most iconic index-mineral assemblages in metamorphic petrology. Almandine porphyroblasts nucleate and grow within a foliated biotite matrix as the parent pelite crosses the garnet-biotite isograd, typically at temperatures around 500 – 600 °C. Geologists use the composition of coexisting garnet and biotite as a classic geothermometer.

Formula
Almandine Fe₃Al₂(SiO₄)₃ in biotite K(Mg,Fe)₃AlSi₃O₁₀(OH,F)₂
System
Aggregate (isometric garnet in monoclinic mica schist)
Hardness
2.5 – 7.5 (Mohs, mica soft / garnet hard)
Provenance
USA (New England, Idaho), India, Norway, Australia

References & Sources

Independent mineralogical references used to verify the scientific details above.

Mineral Profile

Fact Sheet

Chemical Formula
Almandine Fe₃Al₂(SiO₄)₃ in biotite K(Mg,Fe)₃AlSi₃O₁₀(OH,F)₂
Crystal System
Aggregate (isometric garnet in monoclinic mica schist)
Mohs Hardness
2.5 – 7.5 (Mohs, mica soft / garnet hard)
Density
2.80 – 3.30 g/cm³
Refractive Index
1.57 – 1.83 (bulk)
Provenance
USA (New England, Idaho), India, Norway, Australia
Color Origin
Dark brown-black biotite matrix with deep red almandine porphyroblasts

Related Crystals

Stones that share this lattice

Explore the full Atlas →

Next in the Atlas

Garnet in Staurolite

Two crystal habits that only share a schist.