Arkose: Identification, Properties & Value

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

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.

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.

Arkose occurs in many sedimentary settings worldwide; exact locality should be verified from field notes, maps, or specimen provenance.

Arkose is usually valued for teaching, field context, locality, texture, fossils, color, or unusual structures rather than high gem value.

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.