Rocks!!! Ch. 3

What is a rock? Any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet 3 types Igneous Sedimentary Metamorphic Do you think that the minerals we need in our diets are the same as the minerals that make rocks? No, rock minerals are naturally occurring inorganic minerals What does the word Sedimentary tell you about how the rock is formed?

The rock cycle Interactions among Earth’s water, air, land, and living things can cause rocks to change from one type to another A continuous process

Igneous Rocks Forms when lava or magma hardens. Lava: Magma: Molten rock on the surface of the Earth Magma: Molten rock beneath Earth’s surface.

Igneous Rock Formation Igneous rocks are formed by the cooling of molten rocks and the crystallization of minerals.

Types of igneous rocks Intrusive Igneous rock: forms when magma hardens beneath Earth’s surface Extrusive Igneous Rock: forms when lava hardens on the surface of the Earth

Classifying igneous rocks Igneous Rocks are classified based on their texture and composition.

Texture classification Texture: size, shape, and arrangement of interlocking crystals. Course Grained: slow cooling, large crystals. Fine Grained: rapid cooling, small interconnected mineral grains. Glassy: looks like glass, extrusive igneous rocks. Ex. Obsidian Porphyrite: large crystals embedded in a matrix of much smaller crystals.

Composition classification Composition: based on proportions of light to dark minerals Basaltic Composition Contains many dark silicates minerals and plageoclase feldspar Rich in magnesium and iron Ex: basalt and gabbro Granitic Composition Made almost entirely of light-colored silicate minerals like quartz and feldspar 0 to 25% dark minerals Biotite and amphibole

Composition classification Andesitic Composition Between basltic and granitic composition At least 25% dark minerals Ultramafic Composition Composed mainly of iron and magnesium rich mineral Almost entirely dark minerals

Igneous chart Composition and Texture Granite Andesitic Basaltic Ultramafic Coarse Diorite Gabbro Peridotite Fine Phyolite Andesite Basalt Kematite Porphyritic Inside any given rock Uncommon Glassy Obsidian, Pumice

What is a Sedimentary rock? Forms when existing rocks are broken down into sediment then compacted and cemented together Processes Cementing Compaction

How do they form? Weathering: Any process that break rocks into sediments Erosion : The removal of weathered rocks Deposition: when an agent of erosion (water, wind, ice, or gravity) loses energy, it drops the sediment Compaction: is a process that squeezes or compacts sediments together Cementation: takes place when dissolved minerals are deposited in the tiny spaces among the sediments

Classification of sedimentary rocks Classified by the way they form Clastic or chemical

Clastic sedimentary rocks Made of weathered bits of rocks and minerals Grouped according to the size of the sediment.

Clastic sedimentary rocks Texture Sediments Name of Rock Coarse (over 2 mm in size) Gravel - rounded Conglomerate Gravel- angular Breccia Medium (2mm to 1/6 mm) Sand Sandstone Fine (1/16 to 1/256 mm) Silt Siltstone Very Fine (< 1/256 mm) Mud Shale/mudstone

Chemical sedimentary rocks Form when dissolved minerals precipitate from water solution Biochemical Sedimentary Rock: made from once living organisms (like shells and skeleton remains) Ex: limestone, chalk, conquina, rock salt, and bituminous coal

What is a metamorphic rock? Form when existing rocks are changed by heat and pressure Metamorphism: means “change form”

What causes metamorphism? Heat: provides the energy needed to drive chemical reactions which causes existing minerals to recrystallize Pressure: applied in all directions on a rock which causes spaces between mineral grains to close Hydrothermal Solutions: hot, water based solutions that promote recrystallization by dissolving original minerals and then depositing new ones

Classification of Metamorphic Rocks Classified by texture and composition Foliated Rock with layered or banded appearance Ex: Gneiss Nonfoliated No layered or banded appearance Contains only one mineral Ex: Marble

Classification of foliated metamorphic rocks Name Texture/Grain Size Parent Rock Slate Very fine Shale, mudstone Phyllite Fine Schist Medium to course Gneiss Coarse Schist, granite

Classification of non-foliated metamorphic rocks Name Texture/grain size Parent rock Marble Medium to coarse Limestone Quartzite Quartz, sandstone Anthracite Fine Coal