Hydrogrossular Garnet Identification Guide
How to identify hydrogrossular garnet, the massive jade-like grossular, by its compact green-pink color, garnet hardness, and lack of crystals.
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What Hydrogrossular Garnet Looks Like
Hydrogrossular is a hydrous, massive variety of grossular garnet (a calcium-aluminum garnet with OH replacing some silica). Unlike typical gem garnets, it almost never forms visible crystals:
- Color: green (most famous), pink, white, gray, or bluish-green; often mottled with darker spots
- Luster: vitreous to greasy or waxy when polished
- Transparency: translucent to opaque
- Habit: massive, compact, granular aggregate — no individual crystal faces
It is widely sold as "Transvaal jade" or "African jade" because of its jade-like look.
Step-by-Step Field ID Checklist
- Note the massive texture. A compact, fine-grained green-to-pink stone with no crystal faces is the first clue.
- Look for dark spots. Many green specimens carry small black magnetite or chromite inclusions.
- Test hardness. Mohs 6–7.5; scratches glass readily.
- Check for no cleavage. Garnet breaks with a conchoidal to splintery fracture.
- Feel the heft. It is fairly dense (~3.1–3.5 g/cm3).
Key Diagnostic Tests
- Hardness: 6–7.5; harder than nephrite jade in many specimens.
- Cleavage: none; fracture conchoidal to uneven.
- Streak: white.
- Density: ~3.1–3.5 g/cm3, lower than anhydrous grossular because of water content.
- No acid reaction.
- Refractive index lower than dry grossular, a clue for gemologists.
Common Look-Alikes
- Jade (jadeite/nephrite): the big one. Nephrite is tougher and slightly softer (6–6.5) with a fibrous feel; jadeite shows a granular sugary texture. Hydrogrossular's dark magnetite specks and isotropic character help separate it; under a polariscope hydrogrossular is isotropic while jades are aggregates.
- Idocrase (californite): very similar green massive stone; usually anisotropic and slightly softer.
- Chrysoprase: chalcedony, hardness 7, no dark specks, more even apple-green.
- Serpentine: much softer (2.5–5) and greasy.
- Aventurine quartz: shows sparkly mica flakes rather than black mineral spots.
Where It Is Found
The classic source is the Bushveld region of South Africa (hence "Transvaal jade"). Other notable localities include Mali, New Zealand, Canada, Italy, and Pakistan, typically in rodingites, skarns, and altered calcium-rich igneous and metamorphic rocks.
Frequently asked questions
How can you tell if it's real hydrogrossular garnet?
Look for a massive (crystal-free) green or pink stone with vitreous-to-greasy luster, hardness 6–7.5, no cleavage, often peppered with small black mineral spots. Under a polariscope it is isotropic, which separates it from jade and idocrase.
Is hydrogrossular garnet the same as jade?
No. It is a calcium-aluminum garnet often sold as 'Transvaal jade' or 'African jade,' but it is mineralogically different from true jadeite and nephrite jade. Its black inclusions and isotropic optics help distinguish it.
What does hydrogrossular garnet look like?
It looks like a compact, opaque-to-translucent green, pink, or white stone resembling jade, usually with mottled coloring and small dark spots, and no visible crystal faces.
Hydrogrossular vs jade: how do you tell them apart?
Hydrogrossular is a single isotropic garnet that often contains tiny black magnetite spots, while jadeite and nephrite are anisotropic aggregates with granular or fibrous textures. A polariscope and the dark inclusions are the quickest tells.