Opal-quartz, also known as common opal or quartz-opal, is a microcrystalline variety of silica that lacks the characteristic play-of-color seen in precious opal. It is frequently found in hydrothermal veins and sedimentary deposits where it forms massive or botryoidal masses.

Hardness

6.5-7

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralcommonQuartz family

Opal-quartz

Hardness: 6.5-7
Luster: Vitreous
Streak: White
Transparency: Translucent

No image

Is this opal-quartz?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch opal-quartz with a known reference. Opal-quartz sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Opal-quartz leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Opal-quartz typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, gray, brown, red, yellow.
5
Look at form & habit
Crystal system: trigonal. Typical habit: massive.

Often confused with

Opal-quartz vs. its common look-alikes — and how to tell them apart in the field.

How to tell apart: Luster reads vitreous on Opal-quartz and waxy on Chalcedony.

Often found alongside opal-quartz

Minerals reported to co-occur with opal-quartz. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: SiO₂
Mohs hardness: 6.5-7
Density: 2.65 g/cm³
Colors: White Gray Brown Red Yellow
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Trigonal
Crystal habit: Massive
Cleavage: None
Rarity: Common
Uses: Lapidary, Collector
Host rock: Hydrothermal Veins
Typical price: $5-30 per piece

Where rockhounds find opal-quartz

1 mapped spots

Classic worldwide localities

Mexico
Brazil
USA
Madagascar

Field-hunting tip

Look in hydrothermal veins country — that is the host setting where opal-quartz typically forms. If you start seeing quartz, chalcedony, calcite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Texas — start trip planning there.

Browse 1 U.S. spots for opal-quartz →

Common questions

How do you identify opal-quartz?+

Mohs hardness is 6.5-7. It typically shows a vitreous luster. The streak is white. Common colors include white, gray, brown, red.

Where is opal-quartz found?+

Notable localities include Mexico; Brazil; USA; Madagascar.

Can I find opal-quartz in the United States?+

RockHoundR maps 1 opal-quartz rockhounding spots across 1 U.S. states — the top states are Texas.

How much is opal-quartz worth?+

Typical asking prices fall in the range of $5-30 per piece. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like opal-quartz?+

Opal-quartz is most often confused with Opal, Chalcedony, Quartz. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with opal-quartz?+

Opal-quartz commonly co-occurs with Quartz, Chalcedony, Calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does opal-quartz form in?+

Opal-quartz typically forms in hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is opal-quartz used for?+

Opal-quartz is used in lapidary, collector.

Find opal-quartz on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.