Sedimentary Rock Textures

Clastic Textures

• Sedimentary rock names like conglomerate, sandstone, siltstone, and shale are based on grain size.
• More precise naming exists within categories, based on sediment features beyond grain size.
• Breccia differs from conglomerate due to clast angularity.
• Sandstone is a clastic rock with sand-sized grains, regardless of mineral composition.
• Arenite is sandstone composed almost entirely of quartz.
• Arkose is sandstone containing significant feldspar mixed with quartz.
• Lithic wackes contain feldspar, quartz, clay, and dark mineral/rock fragments, representing immature sediments.
• Clastic sedimentary rocks are classified by grain size.
• Sandstones consist of sand-sized grains.
• Shale is a layered rock of fine mud-sized grains, too small to see without magnification.

Chemical Textures

• Naming chemical sedimentary rocks depends on their mineral composition.
• Limestones are mostly calcite.
• Rock salt is composed of minerals like halite.
• Gypsum rock contains gypsum.
• Chalcedony contains microcrystalline quartz, with grains too small to distinguish without a microscope.

Biochemical Textures

• Biochemical sedimentary rocks form from past life, like fossils, shells, or plant remains.
• Coal is made of plant remains.

Sedimentary Rock Types

• Conglomerate is a clastic rock, and is composed of gravel coarse grains (>2mm) that are rounded and poorly sorted.
• Breccia is a clastic rock, and is composed of gravel coarse grains (>2mm) that are angular and poorly sorted.
• Sandstone is a clastic rock, and is composed of medium sand grains (0.0625-2mm) that are variable and variably sorted.
• Siltstone is a clastic rock, and is composed of fine grains (0.004-0.0625mm) that are variable and well sorted.
• Shale is a clastic rock, and is composed of extra fine grains (<0.004mm) that are not visible and well sorted.
• Limestone is a biochemical rock, and reacts to HCI and formed in a warm shallow ocean
• Fossiliferous limestone is a biochemical rock containing visible fossils that reacts to HCI and formed in a warm shallow ocean
• Dolostone is a chemical precipitate rock that reacts to HCI only when powered and formed in a saline lagoon
• Travertine is a chemical precipitate rock that is gray or brown, porous and reacts to HCI, formed in an evaporated spring or cave water
• Chalk is a chemical precipitate rock that is white and powdery and reacts to HCI, formed in warm shallow ocean
• Chert is a chemical precipitate rock that has a conchoidal fracture, formed in a deep ocean floor
• Jasper is a chemical precipitate rock that is red in color and has a conchoidal fracture, formed in a deep ocean floor
• Flint is a chemical precipitate rock that is black in color and has a conchoidal fracture, formed in nodules in limestone
• Agate is a chemical precipitate rock that is layered and translucent and has a conchoidal fracture, formed in nodules in volcanic rocks
• Diatomite is a chemical precipitate rock that is white and powdery, formed in lakes in volcanic environments
• Coal is a biochemical rock that is black, soft and has a low density, formed in heavily vegetated swamp
• Rock Salt is a chemical precipitate that taste like salt and has cubic crystals and cleavage, formed in an evaporating water body
• Gypsum rock is a chemical precipitate that is softer than a fingernail formed in an evaporating water body

Uses of Sedimentary Rocks

• Sedimentary rocks serve as building stones, though less durable than igneous/metamorphic types.
• They are used in construction, including sand and gravel for concrete and asphalt.
• Sedimentary rocks provide economically valuable resources, such as iron ore and aluminum.