Identification guide · Quartz Family
How to Identify Quartz
Quartz forms hexagonal prisms typically capped with pyramidal terminations, ranging from colorless to milky white, purple, yellow, brown, pink, or black depending on trace impurities and irradiation. Its luster is vitreous, streak is white, and hardness of 7 lets it scratch glass and steel easily, a reliable field test since few common minerals match that hardness. It shows no cleavage, breaking instead with a smooth conchoidal fracture, and often displays natural striations running perpendicular to the crystal's length. Quartz is frequently confused with calcite or topaz, but its hardness readily separates it from the much softer calcite.
Quartz identification checklist
| Color | Colorless, White, Purple (amethyst), Yellow (citrine), Pink (rose), Brown/black (smoky) | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous, greasy on fracture surfaces | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Transparent to translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 7 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | None (rare parting on rhombohedral planes) | |
| Fracture | Conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.65 | Ordinary rock-like heft (specific gravity about 2.65), similar to quartz. |
| Crystal system | Trigonal |
Extra tests for Quartz
Glass check. Quartz shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Quartz look-alikes and how to tell them apart
Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Quartz vs Feldspar →
Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Quartz vs Clear Quartz →
Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Quartz vs Smoky Quartz →
Quartz is harder (Mohs 7) than Calcite (Mohs 3), so Quartz will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Quartz vs Calcite →
Is my Quartz real?
- Hardness: real Quartz sits at Mohs 7. Glass imitations are about 5.5, so genuine Quartz scratches glass while a glass fake cannot.
- Bubbles: round gas bubbles under a 10x loupe mean glass or resin, never a natural stone.
- Color: dyed material concentrates color in cracks and pores; look for pigment collecting at the edges of fractures.
- Temperature: natural crystals feel cool and take longer to warm in your hand than plastic or resin.
Quartz identification FAQ
How can you tell if a rock is Quartz?
Check the color (colorless, white, purple (amethyst), and yellow (citrine)), the vitreous, greasy on fracture surfaces luster, a Mohs hardness of 7 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Quartz?
Quartz has a Mohs hardness of 7. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Quartz and Feldspar?
Quartz (Mohs 7, vitreous, greasy on fracture surfaces luster) and Feldspar (Mohs 6–6.5, vitreous to pearly luster) look alike, but hardness, streak and heft usually separate them. See the full Quartz vs Feldspar comparison for a side-by-side table.
How do I know if my Quartz is real?
Real Quartz matches the hardness listed above, shows no round gas bubbles under magnification, and does not concentrate dye in cracks. Glass and resin fakes fail at least one of those checks.
Is Quartz worth anything?
Entry-level Quartz specimens sell for around $5, typical collector pieces about $35, and premium examples $250 or more depending on size, quality and locality.
What color is Quartz?
Quartz is most often colorless, white, purple (amethyst), and yellow (citrine). Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
