Amethyst

Related: Quartz Varieties

AgateAmetrineAventurineBloodstoneCarnelianChalcedonyChrysopraseCitrineHawk's EyeOnyxPrasioliteRock CrystalRose QuartzSmoky QuartzTiger's Eye

Key Differentiators

• 'Bull's eye' optic figure
• RI and SG specific to quartz
• Characteristic color zoning

Natural vs. Synthetic

Synthetic amethyst is commercially available (Hydrothermal). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

• Microscopy — inclusions: Parallel two-phase inclusions in planar growth zones (sometimes called 'tiger stripe'), arranged in parallel growth planes — characteristic of natural amethyst. Also: irregular Brazil-law twinning, hematite/goethite/rutile inclusions, fingerprint healed fractures. Synthetic: Seed plate visible as straight rectangular line, often marked by irregular void inclusions along the seed boundary. Regular parallel growth lines from seed. Brazil-law twinning present but lacks tiger-stripe inclusions. Generally inclusion-free.
• UV Fluorescence: Usually inert to very weak dull reddish-brown (LWUV). Not diagnostic. Synthetic: Typically inert. UV is not useful for amethyst origin determination.
• RI / SG: RI 1.544/1.553; SG ~2.65. Synthetic: Identical — confirms quartz species but does NOT distinguish natural from synthetic. Rely on microscopy.

Commonly Confused With

Commonly confused with: Fluorite.

Treatments

• Heat Treatment → Citrine (if yellow/orange)
• Irradiation (to deepen color)

Price Context

Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.

About Amethyst

The purple variety of quartz, its color is caused by iron impurities and irradiation. Ametrine is a natural bicolor variety showing distinct zones of both amethyst (purple) and citrine (yellow-orange) within a single crystal — most commercial material is from Bolivia.