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, 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.