Rock & Mineral Encyclopedia

Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.

Siltstone

A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.

A soft, green iron-potassium mica that forms in marine sediments and gives greensand its characteristic olive color.

A green, glauconite-rich marine sandstone that records slow deposition on continental shelves and is used as a soil amendment.

A very fine-grained sedimentary rock made mostly of clay minerals, smooth to the touch and lacking the gritty feel of siltstone.