Kerimasite Identification Guide
Identify Kerimasite, a rare zirconium-rich garnet, by its brown color, garnet form, and carbonatite-skarn setting.
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What Kerimasite Looks Like
Kerimasite is a rare zirconium-bearing garnet (in the schorlomite-kimzeyite group). It is typically dark brown, reddish-brown, to nearly black, with a vitreous to resinous luster and translucent-to-opaque diaphaneity. Like other garnets it forms isometric crystals (dodecahedra, trapezohedra) or anhedral grains. Because it is rich in Zr, Ti, and Fe, it tends toward the dark, "melanite-like" end of garnet appearance.
Quick visual cues
- Dark brown to black equant grains/crystals
- Garnet form: rounded dodecahedral/trapezohedral faces
- Glassy-to-resinous luster
- Hosted in carbonatites and associated skarns
Step-by-Step Field ID Checklist
- Confirm garnet form. Isometric, no cleavage, conchoidal fracture.
- Note the dark brown-black color, distinct from the red of common garnets.
- Check the host rock. Kerimasite occurs in alkaline/carbonatite complexes and skarns—an important contextual clue.
- Test hardness. Hard (Mohs ~7-7.5), scratches glass readily.
- Heft it. High density (~3.7-4.0) thanks to Zr and Fe.
- Streak test. Pale brown to white streak (not metallic).
Key Diagnostic Tests
- Mohs hardness: ~7-7.5.
- Density: high, roughly 3.7-4.0 g/cm^3 (heavier than common silicate rocks).
- Cleavage/fracture: none/conchoidal to uneven.
- Streak: white to pale brown.
- Acid: no effervescence (helps separate from associated carbonate matrix, which fizzes).
- Definitive ID: requires microprobe/XRD—Zr content distinguishes kerimasite from titanian schorlomite/andradite.
Common Look-Alikes and How to Tell Them Apart
- Schorlomite (Ti-garnet): nearly identical dark garnet; kerimasite is the Zr-dominant analogue—separated only by chemical analysis.
- Kimzeyite: also a Zr-rich garnet; distinguished by detailed site chemistry (lab).
- Melanite/andradite: black Ti-andradite looks similar but lacks essential Zr.
- Magnetite: also dark and dense but is metallic, magnetic, and gives a black streak—kerimasite is non-metallic, non-magnetic, white-streaked.
Where It Is Found
The type locality is the Kerimasi volcano, Tanzania, in carbonatite-related skarns. Comparable Zr-garnets occur in alkaline igneous and carbonatite complexes worldwide. It is strictly a collector/research mineral.
Frequently asked questions
How do you identify Kerimasite?
Look for dark brown-to-black isometric garnet crystals with no cleavage, a hardness of about 7-7.5, high density (3.7-4.0), and a non-metallic white streak, occurring in carbonatites and skarns; chemical analysis confirms its zirconium content.
What is Kerimasite made of?
It is a zirconium-rich silicate garnet of the schorlomite-kimzeyite group, with essential calcium, zirconium, iron, and silicon, which gives it its dark color and high density.
Kerimasite vs schorlomite—how are they different?
They look almost identical as dark garnets, but kerimasite is zirconium-dominant while schorlomite is titanium-dominant; only microprobe or X-ray analysis reliably separates them.
Is Kerimasite magnetic?
No, it is essentially non-magnetic and gives a white-to-pale-brown streak, which separates it from dark, magnetic, black-streaked magnetite.