Sanidine is the high-temperature form of potassium feldspar typically found as phenocrysts in rapidly cooled volcanic rocks like rhyolite and trachyte. Collectors prize clear, glass-like crystals often embedded in fine-grained volcanic matrices, which are easily distinguished from orthoclase by their optical properties and geological occurrence.
Is this sanidine?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch sanidine with a known reference. Sanidine sits at Mohs 6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Sanidine leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Sanidine typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray, pale yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular, prismatic, or blocky crystals.
Often confused with
Sanidine vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside sanidine
Minerals reported to co-occur with sanidine. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (K,Na)AlSi₃O₈
- Mohs hardness
- 6
- Density
- 2.55-2.63 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular, Prismatic, Or Blocky Crystals
- Cleavage
- Perfect {001}, Good {010}
- Rarity
- Common
- Uses
- Collector, Geological Research
- Host rock
- Rhyolite, Trachyte, And Phonolite Volcanic Rocks
- Typical price
- $10-50 per specimen
Where rockhounds find sanidine
1 mapped spotsClassic worldwide localities
- Eifel Mountains, Germany
- Monte Somma, Italy
- Clear Lake, California, USA
- Auvergne, France
Field-hunting tip
Look in rhyolite, trachyte, and phonolite volcanic rocks country — that is the host setting where sanidine typically forms. If you start seeing quartz, biotite, hornblende in float, you are in the right ground. Field specimens usually show a tabular, prismatic, or blocky crystals habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Mexico — start trip planning there.
Common questions
How do you identify sanidine?+
Where is sanidine found?+
Can I find sanidine in the United States?+
How much is sanidine worth?+
What rocks look like sanidine?+
What minerals are found with sanidine?+
What kind of rock does sanidine form in?+
What is sanidine used for?+
Find sanidine on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
