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Crystal Structure
Ca₃Fe₂(SiO₄)₃.
External databases provide CIF (Crystallographic Information File) downloads + interactive 3D viewers. AMCSD: American Mineralogist Crystal Structure Database (free, RRUFF-hosted). COD: open community-curated database.
Elemental Composition (by mass)
| Element | Mass % | Visual |
|---|---|---|
| O Oxygen | 37.78% | |
| Ca Calcium | 23.66% | |
| Fe Iron | 21.98% | |
| Si Silicon | 16.58% |
Computed from simplified end-member formula. Solid-solution series, water content, and trace substitutions cause real-world variation.
IMA Abbreviation (Whitney-Evans 2010)
Adr
→ Andradite
Garnet
Standard symbol from American Mineralogist (Whitney & Evans, 2010). Used in thin-section labeling, phase diagrams, and IMA-style species records.
Pronunciation
/ænˈdrædaɪt/
↔ an-DRAD-ite
for d'Andrada
Diaphaneity (Transparency)
transparent-to-translucent
Demantoid (gem) transparent; melanite opaque.
Type Locality
Drammen / Norway
Described 1868 by Dana (named for J.B. d'Andrada)
Magnetism
Category:
weakly paramagnetic
Test result:
Detectable pull
Ca-Fe garnet — Fe gives susceptibility.
Test with rare-earth magnet (N42 or N52 neodymium). Suspend specimen on thread for sensitive paramagnetic detection. Diamagnetic minerals are weakly repelled (visible only with strong magnets like bismuth).
Specific Gravity
3.81–3.87
g/cm³
medium
Including demantoid.
For comparison: water = 1.00, glass ≈ 2.5, quartz = 2.65, corundum ≈ 4.00, galena ≈ 7.50, gold ≈ 19.3.
Characteristic Inclusions
Horsetail (byssolite)solid★ diagnostic
Diagnostic of demantoid andradite from Russia.
★ Diagnostic inclusions are characteristic enough to help identify origin or species under 10× loupe.
Market availability: Uncommon
Found at major shows and select dealers. Quality varies by locality.
Collector tier: Solid Display
Reliable mid-tier display species. Easy to find in well-formed examples; broad locality diversity.
Mohs 6.5–7
Vickers (~) 1400 HV
Knoop (~) 1100 HK
Geological setting
Skarn
Element composition by mass
Formula: Ca₃Fe₂(SiO₄)₃ · molar mass: 508.17 g/mol
| O | 37.78% | |
| Ca | 23.66% | |
| Fe | 21.98% | |
| Si | 16.58% |
Computed from atomic weights (IUPAC 2021). Site-occupancy groups (Fe,Mn) split equally.
GroupGarnet Group
Optical Effects
diamond, demantoid)">High dispersion
Mohs Hardness
6.5–7
Andradite sits at 6.5–7 on the Mohs scale — harder than glass; scratches steel.
Colors:
Streak
White
White
Crystal system
Isometric (Cubic)
Isometric (Cubic)
Type localityDrammen, Buskerud, Norway
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Discovery First described 1868 by Dana (Brazil)
SilicatesSilicates (Nesosilicates)
TL;DR · 1 min read
Andradite (Ca₃Fe₂(SiO₄)₃) is the calcium-iron end-member of the garnet group and the parent of one of the most prized gem garnet varieties — demantoid, the brilliant emerald-green chromium-bearing variant from Russia and Madagascar. Andradite's strong dispersion gives demantoid a fire that exceeds diamond, making it the most valuable garnet.
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Andradite (Ca₃Fe₂(SiO₄)₃) is the calcium-iron end-member of the garnet group and the parent of one of the most prized gem garnet varieties — demantoid, the brilliant emerald-green chromium-bearing variant from Russia and Madagascar. Andradite’s strong dispersion gives demantoid a fire that exceeds diamond, making it the most valuable garnet. Black “melanite” (titanium-rich) andradite is a classic skarn species; topazolite (yellow) is rarer collector material.
More minerals to explore #
Willemite (硅锌矿)
Trigonal
Uvarovite (钙铬榴石)
Isometric (Cubic)
Andalusite (红柱石)
Orthorhombic
Fayalite (铁橄榄石)
Orthorhombic
Grossular (钙铝榴石)
Isometric (Cubic)
Spessartine (锰铝榴石)
Isometric (Cubic)
Other Members of the Garnet Group
石榴石族
- Almandine (铁铝榴石)
- Grossular (钙铝榴石)
- Pyrope (镁铝榴石)
- Spessartine (锰铝榴石)
- Uvarovite (钙铬榴石)