ROCKS AND MINERALS PSC 1515 CHAPTER 7

Minerals Naturally occurring Inorganic (contains metal elements – left side of PT) Crystalline – specific 3-D orientation of all atoms Definite (specific) composition (has a specific chemical formula)

Polymorphs Also knows as allotropes Same chemical element but different forms Ex: oxygen has two allotropes Oxygen, O2, and ozone, O3 Ex: carbon has 3 allotropes – graphite, diamond, fullerene

Properties of Minerals Crystal form Hardness Cleavage – does it break into specific lines Luster Color Specific Gravity (density) Streak – color of mineral is when it is powered

Types of Rocks Silicates Non- silicates (carbonates, sulfides, oxides) Si and O make up 78% of the material on the surface Sand is one type of silicate rock Ferrosilicate – contains iron Non- silicates (carbonates, sulfides, oxides) Carbonates are made from sea shells, coral, etc.

How minerals form Crystals form From cooling magma – hot liquid rock that exists below the Earth’s crust Hydrothermal solutions that cool Surface water that evaporates From high pressure and temperature

Cooling Magma Magma – semi-liquid rock that exists in the mantle portion of the Earth (below crust) Geothermal Gradient – Temperature goes up the deeper you go by 300C per km depth. Magma less dense than solid rock – rises to surface As it rises – temperature goes down, minerals crystallize out of solution, The slower it cools the larger the crystals Most minerals are made this way

From Water Minerals in water will crystallize out as either the water cools or evaporates. The more slowly the cooling rate, the larger the crystals Hydrothermal solutions – underground water near some hot magma. As hot water rises, it cools and minerals crystallize out Different minerals (with different melting points) crystallize out at different depths.

Pressure and Temperature As layers of rock – sediment, lava, etc. – get covered by other sediments, lava, etc., they get squeezed together. As pressure and temperature increase some rocks and minerals change structure – metamorphic Note, it does NOT melt, it changes structure under pressure and temperature below the melting point of the rock or mineral Example – graphite to diamond Limestone to marble

The three allotropes of carbon have three different molecular shapes. In diamonds, each carbon is attached to four other carbons and is tetrahedral. In graphite, the carbons are made of planar six member rings in layers. They are trigonal (3) planar (flat). The layers have weak bonds between them allowing each layer of graphite to slide over the other layers. In the fullerene, carbons are in both five and six member rings in exactly the same pattern as a soccer ball. They are not planar like the atoms in graphite but they are not tetrahedral either. They form balls and tubes.

Rocks A. A solid cohesive (stuck together) mixture of mineral crystals Minerals – specific chemical composition Rocks – physical mixture of minerals B. Uses Tools Building material

Kinds of Rock Igneous – comes from magma Sedimentary - made from layers of sediments Metamorphic – changed rock

Igneous Rock Made from cooling magma Tight crystals Very strong granite Intrusive igneous rocks – formed underground Pushes into existing rock Plutons – large crystals formed Batholith – large group of plutonic rock – forms basis of some mountain ranges Lava – magma that makes it to the surface Extrusive igneous rocks Volcanic rock – very small or no crystals

Classification of Igneous Rocks Classified by size of crystals in rock Coarse – crystals large enough to be seen with eyes Fine – microscopic crystals Glassy – no crystals – a glass like solid - obsidian Porphyrinic – large crystals embedded in fine grained rock

Cooling rates and crystals The longer it takes for a crystal to form the larger the crystal will be Slow cooling Slow evaporation Slow addition of heat and pressure

Igneous Rocks - extrusive

Igneous Rock - Intrusive

Sedimentary Rocks Formed by lithification Rocks worn away by wind and rain (sediment). Wash away until find a place to stop. More eroded rock lands in same place. Pressure from top layers forces bottom layers to join together Cover 75% of crust but only 5% or rocks Layers called strata Fossils – remains of ancient plants and animals that have been caught in the sediments. Replaced by rock atoms

Examples of Sedimentary Rock Sandstone – made from rocks – silicates Limestone – made from coral and sea shells – carbonates Coal – made from living plants that died but did not decay Lignite – youngest - softest Bituminous – sedimentary rock – commonly burned Anthracite – metamorphic rock – very hard, high heat output

Sandstone with sand

Limestone

Coal

Metamorphic Rock Rock formed from igneous or sedimentary rock under high temperature and pressure. *** Rock doesn’t melt, if it melts it becomes igneous Examples – graphite to diamond limestone to marble

The Rock Cycle Melted rock is sent to the Earth’s surface by a volcano. As it rises, it cools and forms igneous rock The igneous rock on the surface undergoes weathering and forms sediments The sediments form layer upon layer and finally rock. Layers continue to build up on top. Pressure and temperature increase Crystalline structure of rock changes (without melting) Forms metamorphic rock which gets melted and the cycle starts over.

Recommended problems Reading check page 209 – most of them are good questions RAT – 1- 6, 9-10