Chrysoberyl Identification Guide

What Chrysoberyl Looks Like

Chrysoberyl (BeAl2O4) is a hard beryllium-aluminum oxide prized as a gem. Typical color is yellow, greenish-yellow, golden, to brown, with two famous varieties: color-change alexandrite (green in daylight, red in incandescent light) and cymophane (cat's-eye chrysoberyl). Luster is vitreous, and stones are transparent to translucent. Crystals are tabular to short prismatic (orthorhombic) and frequently form pseudohexagonal trillings (cyclic twins) — a characteristic six-pointed or wheel-like twin.

Step-by-Step Field ID Checklist

1. Note color. Golden-yellow to greenish-yellow is most common; watch for color change (alexandrite) or a sharp eye (cat's-eye).
2. Look for the twin. Pseudohexagonal "wheel" trillings strongly suggest chrysoberyl.
3. Test hardness — the standout clue. Mohs 8.5, third only to diamond and corundum among common gems; it scratches topaz and quartz with ease.
4. Check luster and transparency. High vitreous luster, often very clean.
5. Feel the heft. Dense (SG ~3.7-3.8).
6. Examine for cat's-eye or color change under different light sources.

Key Diagnostic Tests

• Hardness: 8.5 — the most diagnostic field property; very few stones are this hard.
• Cleavage: Distinct in one direction but rarely seen; conchoidal to uneven fracture.
• Streak: White.
• Density: ~3.7-3.8 g/cm3.
• Optics: Doubly refractive (RI ~1.74-1.75); pleochroic, strongly so in alexandrite.
• Magnetism/acid: Non-magnetic; inert to acid.

Common Look-Alikes and How to Tell Them Apart

• Beryl (despite the name, unrelated): Beryl is softer (7.5-8), lighter (SG ~2.7), hexagonal; chrysoberyl is harder and denser.
• Yellow sapphire (corundum): Harder (9) and denser (~4.0); RI higher. A hardness/density check separates them.
• Citrine / yellow quartz: Much softer (7) and lighter (SG 2.65).
• Yellow topaz: Softer (8), with one perfect basal cleavage and lower RI.
• Synthetic alexandrite / color-change sapphire & spinel: Natural alexandrite's specific green-to-red change, RI ~1.74, and density help, but lab work confirms.

Where It Is Typically Found

Chrysoberyl forms in granite pegmatites and in mica schists and other metamorphic rocks rich in beryllium, and concentrates in alluvial gem gravels. Major sources include Brazil (Minas Gerais and Espirito Santo), Sri Lanka (especially cat's-eye), Russia (the original Ural alexandrite), Madagascar, Tanzania, Myanmar, India, and Zimbabwe.

Field Tips and Common Mistakes

Hardness is the great equalizer here: at 8.5, chrysoberyl outranks nearly everything it could be confused with except corundum and diamond, so if a yellow-green "quartz" or "topaz" easily scratches a quartz plate and resists a topaz point, suspect chrysoberyl. The pseudohexagonal twin is a gift to collectors; a six-pointed star or wheel-shaped trilling is essentially a signature, and the re-entrant notches between twin segments help confirm it. For alexandrite, judge color change under two genuinely different lights (north daylight or an LED versus an incandescent or candle flame); a true green-to-red flip is dramatic, while many imitations only shift weakly or from gray to purple. For cat's-eye, roll the cabochon under a single light source: a sharp, mobile silver band that "opens and closes" indicates fine parallel inclusions. Beware lab-grown alexandrite and color-change sapphire or spinel, which mimic the effect and need refractive index and inclusion study to unmask.