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, 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
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Find sanidine on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
