How to Identify Quartz
Quartz is one of the most common minerals on Earth and the reference point for hardness 7. Its signatures are a glassy luster, six-sided crystals, no cleavage, and the ability to scratch glass and steel.
Quick Facts
- hardness
- 7 (scratches glass and steel)
- streak
- White
- luster
- Vitreous (glassy)
- color
- Colorless, white, smoky, pink, purple, yellow — any
- crystal System
- Trigonal (hexagonal prisms with pointed ends)
- cleavage
- None — conchoidal fracture
- specific Gravity
- 2.65
Where to Find It
Everywhere — quartz is a major component of granite, sandstone, and many other rocks, and it fills veins across most geologic settings. Look for well-formed crystals in vein pockets, cavities, and geodes; for massive quartz in white veins cutting darker rock; and for rounded quartz grains and pebbles in sand, gravel, and beaches worldwide.
What Quartz Looks Like
- Six-sided (hexagonal) prismatic crystals ending in a pointed, pyramid-like tip — the classic quartz 'point'.
- A glassy, vitreous luster on fresh surfaces, like broken glass.
- Conchoidal fracture: curved, shell-like broken surfaces with sharp edges, and no flat cleavage planes.
- Often transparent to translucent; clarity ranges from water-clear to milky.
- Common color varieties: clear (rock crystal), smoky gray-brown, rose pink, milky white, and purple (amethyst).
- Hardness you can feel — quartz will scratch a knife blade and window glass rather than being scratched by them.
Simple Tests to Confirm It’s Quartz
You can do these at home with basic tools. They won’t damage a good specimen.
Scratch-glass hardness test
Drag a sharp edge of the specimen across glass. Quartz (hardness 7) scratches glass cleanly and is unmarked itself. This is the single most decisive quartz test, because most common look-alikes (calcite, feldspar softer varieties, glass) will not scratch glass the same way.
Steel-won't-scratch-it test
Try to scratch the specimen with a steel knife or nail (hardness ~5.5). Quartz is harder, so the steel leaves no scratch (any mark is just metal residue that wipes off). If a knife bites into the specimen, it is softer than quartz — likely calcite or feldspar.
Crystal-habit check
Look for six-sided prisms with pyramidal terminations. Quartz crystals are hexagonal and lack the blocky right-angle cleavage of feldspar or the rhombs of calcite. Well-formed hexagonal points are a strong quartz indicator.
No-cleavage / fracture test
Examine broken surfaces. Quartz breaks with curved conchoidal fractures and has no flat cleavage planes. Feldspar, by contrast, cleaves along two flat surfaces at nearly 90°, and calcite cleaves into rhombs — so flat, mirror-like break faces argue against quartz.
Not sure if your specimen is Quartz?
Get an AI-powered first guess from a photo, then use the tests above to confirm.
Look-Alikes & How to Tell the Difference
Calcite
Softer (hardness 3) — a knife scratches it easily and it fizzes in dilute acid, which quartz never does. Calcite also cleaves into perfect rhombs and can show strong double refraction (doubled image) in clear crystals.
Feldspar
Similar hardness (6–6.5, close to quartz) but feldspar has two good cleavage directions meeting near 90°, giving flat, blocky, often iridescent faces. Quartz has no cleavage and glassy conchoidal fracture. Feldspar is also usually opaque and pink or white, not glassy-clear.
Glass (man-made)
Glass shares a glassy luster and conchoidal fracture but is slightly softer (~5.5) and often shows bubbles, mold seams, or a too-perfect shape. Natural quartz forms hexagonal crystals; glass does not.
Topaz / beryl (as clear points)
Both are harder than quartz (topaz 8, beryl 7.5–8) and have different crystal forms and cleavage. If a 'quartz' point scratches quartz itself, suspect a harder gem mineral and verify with an expert.
Frequently Asked Questions
What is the easiest way to identify quartz?+
Scratch a piece of glass with it. Quartz is hardness 7 and scratches glass cleanly while staying unmarked, and a steel knife will not scratch quartz back. Add a glassy luster, six-sided crystals, and conchoidal (no-cleavage) fracture, and you have a confident quartz ID.
How do I tell quartz from calcite?+
Two quick tests settle it. Calcite is soft (hardness 3) so a knife scratches it, and it fizzes when you drop weak acid or vinegar on it. Quartz is hard (7), does not scratch with a knife, and does not react to acid. Calcite also cleaves into rhombs; quartz has no cleavage.
How can I tell quartz from feldspar?+
Look at broken surfaces. Feldspar cleaves along two flat planes meeting near 90°, producing blocky, sometimes iridescent faces, and is usually opaque pink or white. Quartz has no cleavage — it breaks with curved, glassy conchoidal fractures — and often forms clear hexagonal crystals. They are close in hardness, so use cleavage and crystal form to separate them.
What are the main varieties of quartz?+
By color: clear rock crystal, smoky quartz (gray to brown, from natural irradiation), rose quartz (pink), milky quartz (white, from tiny fluid inclusions), amethyst (purple), and citrine (yellow-orange). There is also microcrystalline quartz — chalcedony, agate, jasper, and chert — where the crystals are too small to see.
Can an app identify quartz reliably?+
A photo app can recognize quartz's crystal shape, luster, and color well and give a strong first guess, but color varieties and look-alikes like glass or feldspar can trip up any visual method. The scratch-glass hardness test takes ten seconds and confirms what a photo cannot — use both together.
Related identification guides
This field guide is educational. Visual identification and simple at-home tests are helpful first steps, but they are not a certified geological, gemological, or meteorite analysis. Verify valuable, hazardous, or scientifically important finds with a qualified expert.