Oligoclase is a common plagioclase feldspar that represents a solid solution between albite and anorthite. It is frequently found in igneous rocks and can exhibit a unique schiller effect known as aventurescence, especially in the variety called sunstone.

Hardness

6-6.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralcommonPlagioclase Feldspar Group family

Oligoclase

Hardness: 6-6.5
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this oligoclase?

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 oligoclase with a known reference. Oligoclase sits at Mohs 6-6.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Oligoclase leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Oligoclase typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless, gray, pale yellow, pale green, reddish.
5
Look at form & habit
Crystal system: triclinic. Typical habit: tabular crystals, massive, granular.

Often confused with

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

Often found alongside oligoclase

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

All properties

Chemical formula: (Na,Ca)(Si,Al)₄O₈
Mohs hardness: 6-6.5
Density: 2.64-2.67 g/cm³
Colors: White Colorless Gray Pale Yellow Pale Green Reddish
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Triclinic
Crystal habit: Tabular Crystals, Massive, Granular
Cleavage: Perfect Basal and Pinacoidal
Rarity: Common
Uses: Collector, Petrological Studies, Lapidary
Host rock: Granite, Granodiorite, Syenite, Pegmatites
Typical price: $5-30 for small samples, $50+ for quality crystalline specimens

Where rockhounds find oligoclase

Classic worldwide localities

Norway
Canada
USA
Russia
India

Field-hunting tip

Look in granite, granodiorite, syenite, pegmatites country — that is the host setting where oligoclase typically forms. If you start seeing quartz, muscovite, biotite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify oligoclase?+

Mohs hardness is 6-6.5. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless, gray, pale yellow.

Where is oligoclase found?+

Notable localities include Norway; Canada; USA; Russia; India.

How much is oligoclase worth?+

Typical asking prices fall in the range of $5-30 for small samples, $50+ for quality crystalline specimens. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like oligoclase?+

Oligoclase is most often confused with Albite, Andesine, Pink Feldspar. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with oligoclase?+

Oligoclase commonly co-occurs with Quartz, Muscovite, Biotite, Hornblende. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does oligoclase form in?+

Oligoclase typically forms in granite, granodiorite, syenite, pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is oligoclase used for?+

Oligoclase is used in collector, petrological studies, lapidary.

Find oligoclase on the map

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