Chrome Diopside Identification Guide

What Chrome Diopside Looks Like

Chrome diopside is the bright green, chromium-bearing variety of the pyroxene mineral diopside (CaMgSi2O6). Its color ranges from a rich forest or emerald green to a slightly bluish or grassy green, deepening as chromium content rises; very dark stones can look almost black in larger sizes. It has a vitreous (glassy) luster and ranges from transparent to translucent. Crystals are typically short, stubby prisms with a squarish cross-section (monoclinic system), but most material is found as anhedral grains or cleavage fragments in matrix.

Step-by-Step Field ID Checklist

1. Note the color. Look for a saturated green that stays green under both daylight and incandescent light (no color change, unlike alexandrite-type stones).
2. Check luster and transparency. Vitreous and often gemmy-transparent in thin pieces.
3. Test hardness. It sits at Mohs 5.5-6.5 — a steel knife will barely scratch it, and it will not scratch quartz.
4. Look for cleavage. Two directions of prismatic cleavage meeting at roughly 87 and 93 degrees (near-right angles) are diagnostic of pyroxene.
5. Feel the heft. Specific gravity is about 3.3-3.4, noticeably denser than quartz but lighter than garnet.

Key Diagnostic Tests

• Hardness: 5.5-6.5. Softer than garnet (7-7.5) and beryl.
• Cleavage: Two good prismatic cleavages at ~87/93 degrees — the single most useful clue separating it from garnet (no cleavage).
• Streak: White to pale greenish-gray.
• Fracture: Uneven to conchoidal where it cuts across cleavage.
• Density: ~3.3-3.4 g/cm3.
• Magnetism/acid: Non-magnetic; no reaction to dilute acid.

Common Look-Alikes and How to Tell Them Apart

• Chrome tourmaline / green tourmaline: Tourmaline is harder (7-7.5), has no cleavage, and shows strong dichroism. Chrome diopside is softer and breaks along its two cleavages.
• Tsavorite / chrome grossular garnet: Garnets are harder (7-7.5), denser (~3.6+), isometric, and lack cleavage. A cut garnet will not show cleavage planes.
• Emerald: Beryl is much harder (7.5-8), lower density (~2.7), and shows hexagonal habit; emeralds are far more included and pricier.
• Peridot: Peridot is yellowish "olive" green with very strong doubling of back facets and no pyroxene cleavage at right angles.
• Diopside vs. green glass: Glass shows no cleavage, often has bubbles, and is singly refractive.

Where It Is Typically Found

Chrome diopside forms in chromium-rich ultramafic and metamorphic rocks. The dominant commercial source is the Inagli (Inagli/Aldan) deposit in Yakutia, eastern Siberia, Russia, where it occurs in kimberlite-related ultramafics. It is also a common indicator mineral in kimberlites worldwide and is reported from Finland, Pakistan, Myanmar, Italy, and parts of East Africa, often as small grains in serpentinized peridotite.

Field Tips and Common Mistakes

The most frequent error is confusing chrome diopside with garnet because both can be deep green and gem-bright. Always check for cleavage: if you can rock the stone in light and catch two flat reflective planes meeting near a right angle, it is a pyroxene, not a garnet. A second pitfall is over-grading dark stones; because chromium absorbs strongly, choose thin, well-lit fragments to judge true hue. When prospecting kimberlite float, chrome diopside grains are usually small (a few millimeters), bright green, and rounded by transport, sitting alongside chrome pyrope and ilmenite. Because it is only moderately hard and brittle, faceted chrome diopside abrades and chips with wear, so an old, scuffed "emerald" full of surface scratches and showing cleavage cracks is more likely chrome diopside than a true emerald. Finally, remember it shows no color change between daylight and incandescent light, which separates it instantly from alexandrite-type material.