1. ROCKS AND MINERALS
PSC 1515 CHAPTER 7

2. 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)

3. 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

4. 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

5. 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.

7. 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

9. 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

10. 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.

12. 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

13. 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.

14. 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

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

16. 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

17. 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

18. 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

19. Igneous Rocks - extrusive

20. Igneous Rock - Intrusive

21. 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

22. 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

23. Sandstone with sand

24. Limestone

25. Coal

26. 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

28. 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.

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