Types of RocksJunhel C. Dalanon, DMD, MAT

SNSCLC – MinglanillaMinglanilla, Cebu, Philippines 6046

Rock

• In geology, rock is a naturally occurring aggregate of minerals and/or mineraloids.

• The Earth's lithosphere is made of rock.• In general rocks are of three types, namely,

igneous, sedimentary, and metamorphic. • Petrology is the scientific study of rocks.

Types of Rocks

• Igneous

• Sedimentary

• Metamorphic

Igneous Rock

Igneous Rock formed from melted rock that has cooled and solidified.

When rocks are buried deep within the Earth, they melt because of the high pressure and temperature; the molten rock (called magma) can then flow upward or even be erupted from a volcano onto the Earth's surface. When magma cools slowly, usually at depths of thousands of feet, crystals grow from the molten liquid, and a coarse-grained rock forms. When magma cools rapidly, usually at or near the Earth's surface, the crystals are extremely small, and a fine-grained rock results. A wide variety of rocks are formed by different cooling rates and different chemical compositions of the original magma. Obsidian (volcanic glass), granite, basalt, and andesite porphyry are four of the many types of igneous rock.

Types of Igneous Rock Obsidian Basalt Rhyolite Andesite Granite Diorite Gabbro Porphyry Pumice Scoria Tuff

Obsidian

Basalt

Rhyolite

Andesite

Granite

Diorite

Gabbro

Porphyry

Pumice

Scoria

Tuff

Sedimentary Rock Sedimentary rocks are formed because of the overburden pressure as

particles of sediment are deposited out of air, ice, wind, gravity, or water flows carrying the particles in suspension. As sediment deposition builds up, the overburden (or 'lithostatic') pressure squeezes the sediment into layered solids in a process known as lithification ('rock formation') and the original connate fluids are expelled.

Sedimentary rocks are laid down in layers called beds or strata. That new rock layers are above older rock layers is stated in the principle of superposition. There are usually some gaps in the sequence called unconformities. These represent periods in which no new sediments were being laid down, or when earlier sedimentary layers were raised above sea level and eroded away.

They contain fossils, the preserved remains of ancient plants and animals. Coal is considered a type of sedimentary rock. The composition of sediments provides us with clues as to the original rock.

Types of Sedimentary Rock Quartz Feldspar Amphiboles Breccia Siltstone Sandstone Calcite Limestone Stromatolites Shale Coal Halite Gypsum

Quartz

Feldspar

Amphiboles

Breccia

Siltstone

Sandstone

Calcite

Limestone

Stromatolites

Shale

Coal

Halite

Gypsum

Metamorphic Rock form while deeply buried within the Earth's crust. The

process of metamorphism does not melt the rocks, but instead transforms them into denser, more compact rocks. New minerals are created either by rearrangement of mineral components or by reactions with fluids that enter the rocks. Some kinds of metamorphic rocks--granite gneiss and biotite schist are two examples--are strongly banded or foliated. (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Pressure or temperature can even change previously metamorphosed rocks into new types.

Types of Metamorphic Rock

• Marble• Slate• Gneiss• Quartzite• Schist

Marble

Slate

Gneiss

Quartzite

Schist