3 Types of RocksDecember 9, 2015

7th grade Chapter 9.3-9.5

Scientist of the Day

Rita Levi-Montalcini• Wanted to be a writer; twin

sister a painter• Friend died of cancer –

decided to be a doctor instead• Lost job in WWII Italy because

she was Jewish• Started working in her

bedroom, then as a refugee• Discovered how nerves grow• Won 1986 Nobel Prize in

medicine

Rocks vs Minerals• Rocks are usually mixtures of minerals and other

componentso Can be 1 mineral or several

• 4 main traits to classify rocks:

1. Mineral composition2. Color3. Texture4. Origin

Rock Origins• 3 major groups for rocks• Determine rock group based on other properties

Igneous rock: formed from cooling magma or lava

Sedimentary rock: forms when particles of other rocks, plants, or animal remains are pressed and cemented together

Metamorphic rock: when a rock is changed by heat, pressure, or chemical change, usually deep underground

Igneous Rocks• Formed from magma or lava, which is high in

silica• When it forms below the crust, it’s called

intrusive• Above the crust, extrusive

Trends (Not Always True):• High in silica = dark rocks• Low in silica = lighter-colored rocks• When it cools quickly, it’s hard to form big

crystals, so very fine grains in the texture.• Hard, dense, and durable = good for arrowheads,

countertops, fortresses

Sedimentary RocksSediment: small, solid particles of rocks or living things

• Sedimentary rocks form when sediment is deposited by water or wind and eventually stuck together

• Usually soft• Sandstone and limestone are important building

materials – sometimes used to make concrete too

Forming Sedimentary Rocks

Weathering & Erosion Deposition Compactio

nCementati

on

3 Types of Sedimentary Rocks

Clastic rock: rock fragments are squeezed together. Classified according to how big the particles are. E.g. conglomerate, shale, sandstone

Organic rock: formed when remains of plants or animals are pressed together. E.g. coal from swamp plants, limestone from shells & skeletons that are high in calcium

Chemical rock: usually formed from solutions. E.g. Rock salt, limestone when it’s from evaporation

Metamorphic Rocks• Start off as sedimentary or igneous rocks, then

are changed by heat, pressure, chemical changes, or a combo of these processes. E.g. marble, slate

• Appearance, texture, and crystal structure of the minerals changes

• Classified by pattern of the grains• Used as building materials, old blackboard, etc.• Most metamorphic rocks are foliated

Foliated: thin, flat layers in a rock