Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Felsite
A general term for light-colored, fine-grained volcanic rocks rich in quartz and feldspar, like rhyolite.
igneous
Conglomerate
A coarse sedimentary rock of rounded pebbles and gravel cemented in a finer matrix, recording ancient rivers and beaches.
sedimentary
Bostonite
A fine-grained, feldspar-rich dike rock with a trachytic texture, essentially a hypabyssal equivalent of trachyte or syenite.
igneous
Andesite
A fine-grained, intermediate volcanic rock common at subduction-zone volcanoes, between basalt and rhyolite in composition.
igneousLithographic Limestone
Extremely fine-grained, even-textured limestone famous for lithographic printing and for preserving exquisite fossils like Archaeopteryx.
sedimentary
Siltstone
A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.
sedimentary
Claystone
A very fine-grained sedimentary rock made mostly of clay minerals, smooth to the touch and lacking the gritty feel of siltstone.
sedimentary
Mudstone
A fine-grained sedimentary rock of compacted clay and silt that, unlike shale, breaks in blocks rather than thin layers.
sedimentary
Calcilutite
A very fine-grained, mud-sized limestone formed from carbonate mud, smooth and dense with conchoidal fracture.
sedimentary
Shale
The most common sedimentary rock, a fissile mudrock of compacted clay and silt that splits into thin layers.
sedimentary
Tuff
A light, porous volcanic rock formed from compacted and cemented ash erupted during explosive eruptions.
igneous
Oolite
A limestone made of tiny spherical ooids, resembling fish roe, formed in warm, agitated shallow seas.
sedimentary
Rhyolite
A fine-grained, silica-rich volcanic rock that is the extrusive equivalent of granite, often pale, banded, or flow-textured.
igneous
Hornfels
A tough, fine-grained, non-foliated rock formed by the intense heat of nearby magma baking surrounding rock at contact zones.
metamorphicPipestone
A soft, fine-grained red metamorphosed claystone, sacred to many Native American peoples and carved into ceremonial pipes.
metamorphic
Tinguaite
A fine-grained green phonolitic dike rock rich in nepheline and aegirine, the hypabyssal equivalent of phonolite.
igneous
Novaculite
An extremely fine-grained, dense siliceous rock famous as Arkansas whetstone, prized for sharpening fine cutting tools.
sedimentary
Basalt
A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.
igneous
Ruin Marble
A fractured fine-grained limestone whose iron-stained crack networks form natural scenes resembling ruined cities and landscapes.
sedimentarySölvsbergite
A fine-grained, sodic alkali-feldspar dike rock with trachytic texture, the silica-saturated counterpart to tinguaite.
igneous
Phyllite
A fine-grained foliated metamorphic rock between slate and schist, recognized by its silky silvery sheen and wavy, crinkled surfaces.
metamorphic
Phonolite
A silica-poor volcanic rock of alkali feldspar and feldspathoids that rings when struck, hence 'clinkstone.'
igneous
Dacite
A fine-grained volcanic rock intermediate between andesite and rhyolite, common at explosive stratovolcanoes.
igneous
Bumblebee Jasper
A vivid yellow-and-black banded stone from Indonesian volcanic vents, colored by sulfur, arsenic minerals and iron oxides, not true jasper.
sedimentary