Schorlomite Identification Guide

What Schorlomite Looks Like

Schorlomite is a rare, titanium-rich member of the andradite garnet group. It is almost always deep black to brownish-black, opaque, with a vitreous to slightly resinous or sub-metallic luster on fresh fractures. When it forms crystals, it shows the classic garnet habits: dodecahedra and trapezohedra (icositetrahedra), often as rounded, equant grains rather than perfect crystals. It commonly occurs as embedded grains in alkaline igneous rocks rather than as showy isolated crystals.

Step-by-Step Field ID Checklist

1. Confirm the color and opacity — uniformly black, opaque, no cleavage faces glinting.
2. Look for crystal shape — equant, isometric (no elongation); rounded 12- or 24-sided forms are a strong garnet clue.
3. Check the host rock — schorlomite favors alkaline/silica-undersaturated rocks: nepheline syenites, ijolites, melilite-bearing rocks, and especially carbonatites. Black garnet in a carbonatite is a major hint.
4. Test hardness — it scratches glass easily (Mohs ~7–7.5).
5. Check the streak — drag on unglazed porcelain; schorlomite gives a pale gray to brownish streak, not black.
6. Look for conchoidal fracture and NO cleavage — garnets break unevenly.

Key Diagnostic Tests

• Mohs hardness: ~7–7.5; harder than schorl tourmaline edges in practice but use carefully.
• Streak: light gray/grayish-brown — distinguishes it from magnetite and ilmenite (black streak).
• Cleavage/fracture: none; conchoidal to uneven fracture.
• Magnetism: generally non-magnetic to weakly magnetic (unlike magnetite, which is strongly magnetic).
• Density: high, ~3.8–3.9 g/cm³ — noticeably heavy for its size.
• Acid: inert in dilute HCl (the host carbonatite will fizz; the garnet grains will not).

Common Look-Alikes and How to Tell Them Apart

• Melanite (Ti-andradite): essentially the same family; melanite has lower TiO₂ than schorlomite. They grade into each other and are hard to separate without chemistry — treat field IDs as "Ti-rich andradite."
• Schorl (black tourmaline): schorl forms elongated striated prisms with triangular cross-section, not equant dodecahedra, and is harder to scratch glass uniformly. Habit is the giveaway.
• Magnetite: strongly magnetic with a black streak and metallic luster; schorlomite is non/weakly magnetic with a pale streak.
• Ilmenite: platy/tabular, sub-metallic, black streak, weakly magnetic; lacks garnet crystal forms.
• Black spinel: octahedral crystals (8 faces) rather than 12/24; chemistry differs.

Where Schorlomite Is Typically Found

Look in alkaline intrusive complexes and carbonatites worldwide: notable localities include Magnet Cove, Arkansas (USA); the Kola Peninsula (Russia); various East African Rift carbonatites; and alkaline complexes in Germany and Italy. It is a niche collector mineral, not something you stumble on in ordinary gravels.