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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, pearly on cleavage.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray, pale yellow, gray, yellowish white, reddish white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: blocky, massive, prismatic.
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
- KAlSi₃O₈
- Mohs hardness
- 6
- Density
- 2.56-2.62 g/cm³
- Streak
- White
- Luster
- Vitreous, pearly on cleavage
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Blocky, massive, prismatic
- Cleavage
- Perfect on {001}, distinct on {010}; parting on {100}
- Rarity
- Common
- Uses
- Collector, Geological research
- Host rock
- Most common in felsic volcanic and hypabyssal rocks as rhyolites, phonolites, trachytes; as spherulites in volcanic glass
Where rockhounds find sanidine
2 mapped spotsClassic worldwide localities
- Tooele, Tooele Co., Utah, USA
- Cottonwood Canyon, Peloncillo Mountains, Cochise Co., Arizona, USA
- Rabb Canyon and near the crest of the Black Range, Grant Co., New Mexico, USA
- Drachenfels, Siebengebirge, Rhine, Germany
- Hohenfels, Mendig, Mayen, around the Laacher See, Eifel district, Germany
- Mt. Dore, Auvergne, and Puy Gros du Laney, Puy-de-Dôme, France
Field-hunting tip
Where it forms: Most common in felsic volcanic and hypabyssal rocks as rhyolites, phonolites, trachytes; as spherulites in volcanic glass. If you start seeing quartz, sodic plagioclase, muscovite in float, you are in the right ground. Typical habit: blocky, massive, prismatic. 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?+
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.
