ROCKS AND MINERALS
Rocks are mixtures of natural chemical compounds called minerals, which form crystals with distinctive shapes. There are three main types of rock. Igneous rock is formed when molten rock cools and hardens, a metamorphic rock is one that has been changed by heat or pressure, and sedimentary rock is generally made from fragments of rock cemented together.
- Slate: This dark rock is created when sedimentary shale is put under intense pressure. It forms thin sheets that can be cut into squares and used for roofing.
- Cockscomb barite: This whitish mineral is often found in veins running through rocks. Its crystals form clusters that can resemble cockscombs (roosters’ head crests).
- Schist: Like slate, schist is created by pressure and heat, which transforms a soft sedimentary rock into a very much harder metamorphic rock.
- Chalk: A type of limestone, chalk is built up from the remains of tiny marine organisms, which sank to the bottom of a tropical sea during the age of dinosaurs.
- Marble: Hard and usually pale, marble is a metamorphic form of limestone. It can be carved and polished into statues, and decorative slabs are used in architecture.
- Calcite: The main mineral in limestone and marble, calcite forms the stalactites and stalagmites seen in limestone caves.
- Limestone: All limestones are made of chalky minerals, particularly calcite. They are easily dissolved by rainwater, creating extensive cave systems.
- Halite: Formed by the evaporation of salt lakes, halite is rock salt – the mineral that we use to flavour our food.
- Biotite: Dark brown biotite is a type of mica, a mineral found in most granites and schists. Its plate-like crystals resemble thin, flaky sheets of hard plastic.
- Eclogite: A dense, heavy metamorphic rock formed deep beneath Earth’s surface, eclogite contains bright green pyroxene and glittering red garnet minerals.
- Tremolite: Thin, transparent, fibrous-looking crystals of tremolite form from limestones that have been subjected to intense heat deep underground.
- Beryl: This very hard mineral forms transparent, often greenish crystals that can be cut to create emeralds and aquamarines.
- Granite: One of the main rocks that form continents, granite results from molten rock cooling slowly deep underground to form big quartz, feldspar, and mica crystals.
- Breccia: This sedimentary rock is made of broken, sharp-edged rock fragments cemented together by finer particles.
- Obsidian: Also known as volcanic glass, this shiny black or dark green rock is formed when molten lava cools too quickly to form crystals.
- Gabbro: This is a coarse, dark, iron-rich, crystalline rock that makes up much of the deep ocean floor.
- Pumice: Gas erupting from volcanoes often forms bubbles inside cooling lava. This can then form pumice, which has so many gas bubbles that it floats on water.
- Corundum: This dull-looking stone is a type of corundum, the hardest mineral after diamond. Its crystals are used to make rubies and sapphires.
- Albite: A pale, sodium-rich form of feldspar, albite is a common ingredient of granite, visible as big, blocky crystals that glint in the sunshine.
- Graphite: Made of pure carbon – like diamond – graphite is a soft, metallic mineral that leaves a dark streak. It is used to make the “lead” in pencils.
- Basalt: Heavy, dark basalt is the fine-grained form of gabbro, created when iron-rich lava from oceanic volcanoes cools quickly, often underwater.
- Sandstone: Sand cemented together by other minerals forms sandstone. This red sandstone was once a desert dune.
- Pyrite: Known as “fool’s gold”, this yellow metallic mineral is actually made of iron and sulfur. It often forms big cubic crystals like the ones seen here.
- Conglomerate: Very like breccia, this rock is a solid, cemented mass of rounded pebbles, like those found on riverbeds and lake shores.
Picture Credit : Google
