monoclinic Inosilicates

Chrome Diopside

CaMg1-xCrxSi2O6

Crystal Structure

CDL Notation

 #! Species: Chrome Diopside (CaMgSi2O6:Cr)
#! System: Monoclinic (2/m)
#! Habit: Short prismatic; vivid green from Cr3+
monoclinic[2/m]:{110}@1.0 + {010}@0.7 + {001}@0.4

Crystal System monoclinic

Point Group 2/m

Crystal Forms (3)

{110} {010} {001}

Quick Facts

Hardness

5.5

Specific Gravity

3.22

Refractive Index

1.664

Optical Character

Biaxial +

Interactive Preview

Open this crystal in the CDL Playground to rotate, export, and explore in 3D.

Open in Playground

Physical Properties

Crystal Systemmonoclinic

Hardness (Mohs)5.5

Specific Gravity3.22

CleavageTwo perfect {110} pyroxene cleavages at ~90°

FractureConchoidal

LustreVitreous

Optical Properties

Refractive Index1.664

Birefringence0.024-0.031

Optical CharacterBiaxial +

Dispersion0.013-0.020

Pleochroismweak: Vivid green / Pale green (Three shades of green; less dramatic than tourmaline or alexandrite)

Colours

Vivid emerald-green to medium green

Localities

Russia (Inagli deposit, Yakutia/Sakha Republic; also described as Sayan Mountains in trade; primary world source)Finland (minor green diopside)Pakistan (chromiferous diopside)Myanmar (minor)Canada (Ontario, Quebec; minor chrome diopside in kimberlites)

Common Inclusions

Silicate and sulfate melt inclusions (from Inagli deposit)Two-phase fluid inclusionsOccasional chromite crystals

Known Treatments

Generally not treatedLow-quality material may be fracture-filled (rare)

Crystal Forms

prismpinacoid

Diagnostic Features

Biaxial positive (distinguishes from emerald biaxial negative, chrome tourmaline uniaxial negative, tsavorite isotropic); moderate birefringence 0.024-0.031 (visible doubling in deeper stones); RI 1.664-1.701 (higher than emerald 1.565-1.602, much lower than tsavorite 1.734-1.759); Chelsea filter red (Cr3+ — same as emerald, NOT diagnostic for separation); Inagli deposit Yakutia as primary source

Notes

Chromiferous variety of diopside (CaMgSi2O6); Cr3+ substitutes for Mg2+ in M1 site. Colour from Cr3+ (same chromophore as ruby and emerald, but different field strength producing green). Monoclinic 2/m. Note: this file is the chromiferous variety; diopside.yaml is the general species entry. Use id: chrome-diopside to avoid collision. Inagli deposit as primary source confirmed by Naumov, Kamenetsky et al. 2008, Geochemistry International 46(6) (DOI 10.1134/s0016702908060025) [VERIFIED]: silicate and sulfate melt inclusions in chrome diopside from Inagli, Yakutia. Gem localities confirmed by Shigley et al. 2000 (DOI 10.5741/gems.36.4.292) [VERIFIED]. Constants from Read 7th ed. (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED]. Key separation from lookalikes: biaxial positive optic sign (emerald biaxial negative; tsavorite isotropic; tourmaline uniaxial negative). RI 1.664-1.701 is intermediate.