Ugrandite Garnet Identification Guide

What Ugrandite Garnet Looks Like

"Ugrandite" is the calcium-garnet series, an acronym for uvarovite, grossular, and andradite - garnets that share calcium in their structure. Colors span the green of chrome uvarovite, the green/honey/cinnamon/colorless range of grossular, and the green, yellow, and black of andradite. Crystals typically form well-shaped dodecahedra or trapezohedra (twelve- to twenty-four-sided), often in or on a contact-metamorphic or skarn host rock. Luster ranges from vitreous to sub-adamantine (especially in andradite/demantoid); transparency runs from gem-clear to opaque.

Step-by-Step Field-ID Checklist

1. Confirm garnet form. Look for isometric crystals - rounded dodecahedra/trapezohedra with no cleavage.
2. Note the host. Ugrandites favor skarns, marbles, and serpentinites rather than schists/gneisses.
3. Assess color. Green (uvarovite/demantoid/tsavorite-grossular), honey-brown (hessonite grossular), or black (melanite andradite).
4. Hardness check. Scratches glass readily; not scratched by a steel knife.
5. Look for conchoidal fracture and absence of cleavage on broken crystals.
6. Weigh in hand. Andradite especially feels dense (high specific gravity).

Key Diagnostic Tests

• Mohs hardness: ~6.5-7.5 (grossular ~7-7.5; andradite ~6.5-7; uvarovite ~6.5-7).
• Streak: White.
• Cleavage/fracture: No true cleavage; conchoidal to uneven fracture.
• Magnetism: Andradite (iron-rich) may show weak attraction to a strong magnet; uvarovite/grossular generally not.
• Acid: No reaction in the garnet itself (a carbonate host marble will fizz).
• Density: Grossular ~3.6, uvarovite ~3.8, andradite ~3.8-3.9 g/cm3 - high for silicates.

Common Look-Alikes

• Pyralspite garnets (almandine, pyrope, spessartine): Visually similar crystals but iron/magnesium/manganese rich, usually red-orange, and found in different rocks. Refractive and density values differ; ugrandites trend toward green/black and skarn hosts.
• Epidote: Green but prismatic with one good cleavage, unlike garnet's blocky no-cleavage habit.
• Vesuvianite (idocrase): Green and skarn-associated but forms stubby prisms, not dodecahedra.
• Peridot/diopside: Have cleavage and lower density.

The combination of isometric no-cleavage crystals, high density, calcium-rich green-to-black colors, and skarn/marble host points to an ugrandite.

Where It Is Found

Ugrandite garnets concentrate in calcium-rich metamorphic settings: skarns, contact-metamorphosed limestones and marbles, and chromite-bearing serpentinites (for uvarovite). Notable localities include the Ural Mountains (Russia) for uvarovite and demantoid, Mexico and Italy for andradite/grossular, and East Africa (Kenya, Tanzania) for green grossular (tsavorite).