Sedimentary Rocks · common
Arkose
Arkose is a feldspar-rich sandstone that often looks pink, reddish, tan, or light gray and may show visible sand-sized grains.
Also known as: Feldspathic sandstone, Arkose sandstone.
Arkose properties at a glance
| Type | Sedimentary Rocks |
|---|---|
| Chemical formula | Quartz and feldspar-rich sandstone |
| Mohs hardness | 6 |
| Luster | dull |
| Streak | Variable; usually light-colored |
| Cleavage | Variable by mineral grains |
| Fracture | Granular |
| Specific gravity | 2.45 |
| Transparency | opaque |
| Common colors | Pink, Red, Tan, Gray, White |
| Rarity | common |
Geology & background
Forms when feldspar-rich sand, often derived from nearby granite or gneiss, is deposited and cemented before the feldspar fully weathers to clay.
Arkose helps geologists recognize nearby crystalline source areas and relatively rapid sediment deposition.
How to identify Arkose
- Look for sand-sized grains with abundant pale, pink, or salmon feldspar.
- Arkose is usually more feldspar-rich and less uniformly quartz-rich than typical sandstone.
- Granular texture and weak bedding can help separate it from granite.
- Fresh surfaces show the grain mix better than weathered surfaces.
Full Arkose identification guide: checklist, home tests and look-alikes →
Arkose vs similar stones
Not sure it isn't something else? Side-by-side comparisons with the stones most often confused with Arkose.
Where Arkose is found
Arkose occurs in many sedimentary settings worldwide; exact locality should be verified from field notes, maps, or specimen provenance.
How much is Arkose worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Arkose is usually valued for teaching, field context, locality, texture, fossils, color, or unusual structures rather than high gem value.
Common uses
- Field identification
- Education
- Depositional environment study
- Local building stone when durable
Interesting facts
- Arkose usually contains noticeably more feldspar than ordinary quartz-rich sandstone.
- Pink or salmon colors often come from potassium feldspar or iron staining.
- It commonly points to rapid erosion near granitic source rocks.
Care & safety
Arkose can be soft, porous, crumbly, or weakly cemented depending on grain size, cement, and weathering.
Avoid inhaling dust. Do not cut, grind, or polish unknown sedimentary rocks without eye protection and a properly rated respirator.
Arkose FAQ
What is Arkose?
Arkose is a feldspar-rich sandstone that often looks pink, reddish, tan, or light gray and may show visible sand-sized grains.
How much is Arkose worth?
Entry-level Arkose specimens sell for around $1, a typical collector specimen for about $10, and premium pieces for $75 or more. Arkose is usually valued for teaching, field context, locality, texture, fossils, color, or unusual structures rather than high gem value.
How hard is Arkose?
Arkose has a Mohs hardness of 6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is Arkose used for?
Arkose is used for field identification, education, depositional environment study, and local building stone when durable.
