Argillite
What is Argillite?
Argillite is a fine-grained sedimentary rock composed primarily of clay minerals. It forms through the compaction of clay-rich sediments, such as shale, but is less consolidated than shale. Argillite is often found in shades of gray, black, brown, red, or green, and can exhibit a variety of textures, from smooth to slightly rough. It is commonly used in carving and is known for its ability to take a high polish. The rock's formation involves the lithification of clay minerals, which are typically deposited in low-energy environments like lakes, lagoons, or deep-sea basins. Over time, the weight of overlying sediments compacts the clay, expelling water and leading to the formation of argillite. It is a relatively soft rock, making it suitable for carving and other artistic applications.
Optical Properties
- Refractive Index
- Variable, typically around 1.52-1.60
- Birefringence
- Variable, depending on the mineral composition
- Pleochroism
- None
- Optical Character
- Biaxial
- Dispersion
- Not applicable
Discover Values
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Argillite before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Argillite Localities Map
See where Argillite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
More Images
Quick Facts
Physical Properties
- Color
- Gray, black, brown, red, green
- Hardness (Mohs)
- 2.5-4
- Density
- 2.6-2.8 g/cm³
- Luster
- Dull to earthy
- Crystal System
- Amorphous
Chemical Properties
- Chemical Formula
- Variable, primarily composed of clay minerals
- Elements
- Si, Al, O, Fe, Mg, Ca, Na, K
Also Known As
Identify Argillite Instantly
- Snap a photo, get instant results
- 6,700+ rocks, minerals & crystals
- Discover collecting spots near you
Argillite FAQs
How do I identify Argillite?
Argillite can be identified by its hardness of 2.5-4 on the Mohs scale, Gray color, Dull to earthy luster, Amorphous crystal system. Look for these key characteristics when examining specimens.
What color is Argillite?
Argillite typically appears in Gray, black, brown, red, green. Color can vary depending on impurities and formation conditions.
How hard is Argillite?
Argillite has a hardness of 2.5-4 on the Mohs scale. This makes it a soft mineral that can be scratched easily.