Chrome-Dravite Identification Guide

What Chrome-Dravite Looks Like

Chrome-dravite (often written chromium dravite) is a chromium- and vanadium-bearing member of the dravite tourmaline series (a magnesium-rich tourmaline). It shows an intense, almost saturated dark green to emerald green color that can appear near-black in thick crystals. Luster is vitreous, and it ranges from translucent to transparent in thin sections. Crystals follow the classic tourmaline habit: elongated prisms with a rounded-triangular cross-section and prominent vertical striations running parallel to the length.

Step-by-Step Field ID Checklist

1. Examine crystal shape. Long prismatic crystals with a distinctly curved triangular cross-section and heavy lengthwise striations strongly suggest tourmaline.
2. Check the color. Deep chromium green; in small fragments hold it to strong light to confirm green rather than true black.
3. Look for striations. Parallel grooves down the prism faces are a tourmaline hallmark.
4. Test hardness. Mohs 7-7.5 — it scratches glass and quartz easily.
5. Check for cleavage. Tourmaline has no cleavage; breaks are conchoidal to uneven.
6. Look for pleochroism. Rotating a transparent piece often shows two different green tones (dichroism).

Key Diagnostic Tests

• Hardness: 7-7.5 (scratches window glass).
• Cleavage: None — a key separator from diopside and other green minerals.
• Streak: White to very pale green.
• Fracture: Conchoidal to uneven, brittle.
• Density: ~3.0-3.1 g/cm3.
• Magnetism/acid: Non-magnetic; inert to acid.
• Optical: Strongly dichroic; pyroelectric/piezoelectric (will attract dust or paper when warmed/rubbed).

Common Look-Alikes and How to Tell Them Apart

• Chrome diopside: Softer (5.5-6.5) and has two right-angle cleavages; chrome-dravite is harder and cleavage-free.
• Verdelite / chrome tourmaline (elbaite): Mineralogically very close; chrome-dravite is the Mg-rich (dravite) end, usually from different deposits, but field separation needs lab chemistry. Both are tourmalines, so habit and hardness match.
• Green grossular garnet (tsavorite): Isometric, no striations, no pleochroism, denser (~3.6).
• Emerald: Hexagonal, no rounded-triangular cross-section, hardness 7.5-8, often with distinctive jardin inclusions.
• Green glass: No striations, no pleochroism, often bubbles; singly refractive.

Where It Is Typically Found

Chrome-dravite is rare. The best-known occurrence is around Tanzania and Kenya (the Commander/Landanai and related East African chromium-rich metamorphic zones), where chromium from associated ultramafic rocks enters the tourmaline structure. Similar chromium dravite has been reported from Russia (the Urals) and other localities where boron-bearing fluids interacted with chromium-rich host rocks. It forms in metamorphosed, chromium-enriched sediments and ultramafics rather than in typical granite pegmatites.

Field Tips and Common Mistakes

Most chrome-dravite in the field is so darkly saturated it reads as black, so the single best habit is to chip or wet a thin edge and backlight it with a bright flashlight: a green glow confirms tourmaline color rather than a true black species like schorl or magnetite. Because dravite and elbaite tourmalines share habit and hardness, do not try to pin the exact species in the field; record it as "chromium green tourmaline" and let chemistry settle dravite versus elbaite. Watch for the rounded-triangular cross-section and parallel striations, which rule out garnet and beryl immediately. A handy confirmation is the pyroelectric effect: gently warm a clean crystal and it will attract tiny paper bits or dust to its ends. Avoid mistaking heavily included or fractured material for poor quality alone; chrome-dravite is collected largely for its rarity and intense color, and even small clean windows are prized.