Crystal Structure
Ca₃Fe₂(SiO₄)₃.
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
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.
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)