Amethyst Identification Guide
A field guide to identifying amethyst, the purple variety of quartz, using color zoning, hardness, and crystal habit, and separating it from fluorite and glass.
Read the full Amethyst encyclopedia entry →
What Amethyst Looks Like
Amethyst is the purple variety of quartz (SiO2). Color ranges from pale lilac to deep reddish-purple ("Siberian" grade), and is almost always unevenly distributed — concentrated in the crystal tips and in angular zones. Luster is vitreous, and transparency runs from transparent to translucent.
The classic habit is a hexagonal (six-sided) prism capped by a six-faced pyramid, but the most common occurrence is as a druzy crust of pointed crystals lining the inside of agate geodes. In geodes the crystals are short and tightly packed, deepening in color toward the points.
Step-by-Step Field-ID Checklist
- Note the color and its distribution. Patchy color zoning and angular color banding are strong signs of natural amethyst.
- Inspect crystal form — six-sided prisms with pyramidal terminations, or a geode lining of purple points.
- Scratch test — it must scratch glass (Mohs 7) and resist a steel knife.
- Check fracture — break surfaces should be conchoidal, glassy and curved, with no flat cleavage planes.
- Look through it — natural amethyst commonly shows color zoning and angular "tiger-stripe" or "zebra" internal banding under a loupe.
Key Diagnostic Tests
- Mohs hardness: 7. Scratches glass and quartz-grade abrasives; a knife will not mark it.
- Streak: white.
- Cleavage/fracture: no cleavage; conchoidal fracture.
- Specific gravity: ~2.65.
- Inert to acid, non-magnetic. Color may fade with strong heat (turning yellow/citrine).
Common Look-Alikes
- Purple fluorite: much softer (Mohs 4), shows perfect octahedral cleavage with flat angled faces, and is scratched by a knife. Fluorite often grows as cubes, never six-sided prisms.
- Glass / imitation: look for gas bubbles, swirl marks, and a complete lack of crystal faces; glass is also softer and may show mold seams.
- Purple sapphire: far harder (Mohs 9) and much denser; rare and typically faceted, not in geode druze.
- Iolite and purple scapolite: usually faceted gems; iolite is strongly pleochroic (changes from blue to clear when rotated) whereas amethyst's pleochroism is weak.
Where It Is Found
Major sources include Brazil and Uruguay (large basalt geodes), Zambia (deep saturated crystals), Russia's Ural Mountains, Mexico (Veracruz prisms), and many U.S. localities such as Arizona's Four Peaks and the Lake Superior region. It forms in volcanic cavities, hydrothermal veins, and pegmatites.
Frequently asked questions
How can you tell if it's real amethyst?
Real amethyst is Mohs 7 (scratches glass, resists a knife), has no cleavage and breaks with conchoidal fracture, and typically shows uneven purple color zoning. Glass imitations have bubbles and no crystal faces; fluorite is soft and cleaves.
What does natural amethyst look like?
It is glassy, transparent-to-translucent purple quartz, often as six-sided prisms with pyramid tips or as a crust of purple points lining a geode, with color deepening toward the crystal terminations.
Amethyst vs purple fluorite — how do I tell them apart?
Hardness and cleavage decide it. Amethyst is Mohs 7 with no cleavage; fluorite is Mohs 4 with perfect octahedral cleavage and is easily scratched by a knife. Fluorite also forms cubes, amethyst forms hexagonal prisms.
Why is some amethyst pale and some deep purple?
Color comes from trace iron plus natural irradiation and varies by locality and growth zone. Color is naturally patchy, which is itself a clue to authenticity; intense even color throughout can indicate dyed glass or synthetics.
Can heat change amethyst?
Yes. Heating amethyst can turn it yellow or orange (producing citrine) or green (prasiolite). Excess sunlight or heat can also fade natural color over time.
Amethyst identified by the community
Recent Amethyst specimens identified with Rock Identifier.
