Common Gemstones: How to Tell Them Apart

Many common gemstones are varieties of the same mineral. Understanding the relationships makes identification much easier.

The quartz family

Most common coloured gemstones sold in markets are varieties of quartz (SiO₂, hardness 7). Purple quartz is amethyst. Yellow is citrine. Pink is rose quartz. Brown-red-yellow banded varieties are jasper and agate. Colourless quartz is rock crystal. The colour differences come from trace impurities and structural variations.

Distinguishing quartz from glass

Glass is softer than quartz (hardness ~5.5 vs 7) — quartz will scratch glass, glass won't scratch quartz. Quartz also feels cooler to the touch initially because it conducts heat away from your skin faster than glass. Real quartz often has visible natural inclusions; glass is typically clean and may have bubbles.

Feldspar varieties

Feldspars are the most abundant minerals in the crust. Moonstone shows adularescence (a floating blue-white sheen). Labradorite has labradorescence (metallic iridescence in blues, greens, and golds). Sunstone contains tiny reflective platelets that produce a glittery effect.

The jade confusion

Two distinct minerals are sold as jade: jadeite (rare, hard, comes in intense greens) and nephrite (more common, waxy surface, greens, whites, greys). Both are tough stones but have different mineral compositions. Most commercial 'jade' is nephrite; Burmese imperial jade is jadeite and very valuable.