Silkstone is a fibrous, microcrystalline variety of quartz characterized by a unique, silky luster that arises from its dense, parallel fiber structure. It is a popular material for lapidary work and cabochons, often found in sedimentary deposits where silica has replaced other materials or filled veins.
Is this silkstone?
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 silkstone with a known reference. Silkstone sits at Mohs 7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Silkstone leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Silkstone typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, gray, yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: fibrous.
Often confused with
Silkstone vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside silkstone
Minerals reported to co-occur with silkstone. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 7
- Density
- 2.65 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Fibrous
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Sedimentary
- Typical price
- $5-50 for slabs and polished specimens
Where rockhounds find silkstone
Classic worldwide localities
- Australia
- USA
- Brazil
- Madagascar
Field-hunting tip
Look in sedimentary country — that is the host setting where silkstone typically forms. If you start seeing quartz, hematite, limonite in float, you are in the right ground. Field specimens usually show a fibrous habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find silkstone on the map
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