Dark gray slate (possibly argillite or shale)

Fine-grained, dull to silky luster, dark gray with rusty weathering patches, and excellent planar cleavage producing thin slabs. Typical hardness is about 3–5 Mohs; no visible crystals or strong reaction to dilute acid.

Formed when shale or mudstone was compressed and metamorphosed at low grade, commonly during mountain building. Its exact geological age cannot be determined from the photograph; formation depends on the local bedrock.

Used for roofing, flooring, paving, wall cladding, writing slates, and landscaping; attractive pieces may be collected but usually have little gem value.

The flat splitting surfaces reflect slate cleavage, which differs from original sedimentary bedding. Rust-colored areas likely represent oxidation of iron-bearing minerals or weathered iron staining.

The image strongly supports slate or slate-like argillite, though shale is possible if the pieces are soft and split along bedding. Common field tests: scratch with a steel nail, inspect fine cleavage, and check that it does not fizz with dilute hydrochloric acid. Around 38.3°N, 48.8°E, slate-like metamorphic rocks are plausible in the mountainous Lesser Caucasus region, but exact identification needs a fresh surface and locality geology.