Milky Quartz Identification Guide
A field guide to identifying Milky Quartz by its cloudy white color, glassy luster, hardness 7, and conchoidal fracture.
Read the full Milky Quartz encyclopedia entry →
What Milky Quartz Looks Like
Milky Quartz is the cloudy white variety of quartz, colored by countless microscopic fluid and gas inclusions trapped during growth. It is one of the most common quartz forms, often seen as white vein quartz.
- Color: White to cloudy gray-white, sometimes with translucent zones.
- Luster: Vitreous (glassy), greasy on broken surfaces.
- Transparency: Translucent to nearly opaque (the milkiness blocks light).
- Habit/form: Massive vein fillings, or six-sided prismatic crystals capped by pyramids when well-formed.
Step-by-Step Field ID Checklist
- Check hardness first: Quartz (7) scratches glass and steel easily and is not scratched by a knife — the single most useful test.
- Look at luster and fracture: Glassy with smooth, curved conchoidal fracture; no flat cleavage faces.
- Inspect for crystal form: If terminated, look for six-sided prisms with pointed ends.
- Note the cloudiness: Even milkiness from tiny inclusions, often denser toward the core of vein material.
- Confirm with the acid and density tests below.
Key Diagnostic Tests
- Mohs hardness: 7 — scratches glass and a steel knife; not scratched by them.
- Streak: White (but quartz is harder than the streak plate, so it tends to powder the plate).
- Cleavage/fracture: No cleavage; conchoidal fracture.
- Density: ~2.65 g/cm3.
- Acid: No reaction to dilute HCl.
- Magnetism: None.
Common Look-Alikes and How to Tell Them Apart
- Milk opal / common opal: Softer (5.5–6.5), lighter, waxy luster; quartz is harder and heavier.
- White calcite / marble: Soft (3), fizzes in acid, and shows rhombic cleavage; quartz does neither.
- White feldspar: Has flat cleavage planes and is slightly softer (6); quartz has no cleavage.
- White chalcedony: Same composition (SiO2) but microcrystalline and waxier; milky quartz shows visible crystalline glassiness and can form large clear-ish crystals.
- Barite: Much heavier (density ~4.5) and softer; quartz is light and hard.
- Howlite: Soft (3.5), chalky, usually gray-veined.
Where It Is Found
Milky quartz is essentially worldwide. It fills veins in nearly every rock type, forms in pegmatites and hydrothermal systems, and is a common pebble in streams and on beaches everywhere granite and metamorphic terranes occur.
Frequently asked questions
How can you tell if it is milky quartz?
Confirm hardness 7 (it scratches glass and a steel knife but they cannot scratch it), a glassy luster with conchoidal fracture, no cleavage, and that it does not fizz in acid. Its cloudy white color comes from microscopic inclusions.
What is the difference between milky quartz and clear quartz?
They are the same mineral; milky quartz is clouded by tiny fluid and gas inclusions that scatter light, while clear quartz (rock crystal) is transparent because it lacks those inclusions.
Milky quartz vs calcite — how to tell them apart?
Calcite is soft (3), fizzes in dilute acid, and has rhombic cleavage; milky quartz is hard (7), does not react with acid, and breaks conchoidally with no cleavage.
What does milky quartz look like?
It is a cloudy white to gray-white, glassy stone, often found as white veins or as six-sided crystals with pointed terminations, translucent at the edges but milky in the body.
Milky Quartz identified by the community
Recent Milky Quartz specimens identified with Rock Identifier.
