Rock

A mixture of two or more minerals

Can form deep inside the earth , on the earth’s crust or in water found on the earth’s surface.

Can form fairly quickly or over millions of years.
Rocks are grouped into three families based on how they are formed.
1. Igneous – forms when molten (melted) rock from inside the earth cools and becomes solid.
2. Sedimentary
– forms when sediment (sand, silt, small rocks, bits of other stuff) get squished or cemented together
3. Metamorphic – when heat, pressure and hot liquid turns one kind of rock into another kind of rock.
Below the earth’s surface, temperature and pressure are very high, so rocks melt. When molten
(melted) rock cools, crystals form. Geologists class igneous rock by where it cools – either above or below the earth’s surface.
Below the earth’s surface:
Magma is molten rock under the earth’s surface. When magma cools and hardens, it is called Intrusive rock . Magma has a chance to cool more slowly, so large, organized crystals have time to form. Ex. granite.
Above the earth’s surface:
Lava – molten rock above the earth’s surface – like what comes out of volcanoes. When lava cools (above the surface) it is called Extrusive rock.
This cools much more quickly, so small crystals are all that have time to form.
Basalt (left) – only small crystals have time to form
Obsidian (right)
– no crystals have time to form, has sharp edges like glass

Quick answers:
1. Where is intrusive rock formed?
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2. Where is extrusive rock formed?
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3. What is the difference between magma and lava?
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Sediment is loose particles – bits of rocks, minerals and decaying plants and animals.
Sediment slowly settles on top of other sediment, on top of other sediment, on top of other sediment
(see the layers in the picture?) in places like oceans or river beds. It forms layers called beds .
The layers get squeezed together, this is called compaction. Sometimes, water soaks into the rock and other minerals dissolve forming a natural cement. This is called cementation.
Geologists class sedimentary rocks by the size of their grains.

Small grains – formed from fine mud and silt - Shale
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Medium grains – formed from sand – Sandstone
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Large particles – formed from small pebbles and stones that are cemented together - in fact, it looks like concrete
– Conglomerate
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Limestone
– formed with shells and skeletons of animals – a great place to find fossils.
Homework:
Reading check, P. 331, 1-4

Below the surface of the earth, where there is a lot of heat, pressure and hot fluids, it can change one kind of rock into another kind of rock. This is called metamorphic rock. Metamorphic rock can be made from any other kind of rock - igneous, sedimentary or another metamorphic rock – this would be called the parent rock.
Ex. If granite (an igneous rock) gets put under a lot of pressure, the mineral grains get squeezed closer together, it becomes gneiss (sounds like “nice”), a metamorphic rock.
Granite Gneiss
(Interesting fact: if you can see this picture in colour, the little rusty red bits in the gneiss are garnet.)
Hot fluids can flow into rocks and change it both physically and chemically. This is a very looooonnnngggg, sloooooowwwwww process. Sometimes the rock changes so much that it doesn’t even look like the parent rock any more.
Parent rock + Heat, Pressure or Hot Liquid  Metamorphic rock
Granite (igneous)

Gneiss
Shale (sedimentary)  Slate
Sandstone (sedimentary)  Quartzite
Limestone (sedimentary)

Marble
Quick answers:
1. What 3 types of rock can become metamorphic?
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2. What are the 3 conditions that form metamorphic rock?
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3. What is a parent rock?
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Homework:
Page 339. Checking concepts. Q. 1-9
Understanding key ideas. Q 10, 11a., 13.

NAME
Sedimentary limestone; sandstone; chalk; coal; shale; conglomerate
Igneous pumice; granite; basalt; obsidian
Metamorphic marble; slate; gneiss; schist; quartzite;
CAUSE
Layers of sediment (mud, sand, gravel and minerals) settle, and are compacted or cemented together over thousands of years
LOCATION
Where oceans or bodies of water once existed or still exist
Molten rock cools either inside the earth’s crust
(magma – intrusive – fast small crystals) or outside the earth’s crust (lava – extrusive
– slow – bigger crystals)
Created when sedimentary or igneous rocks undergo change caused by pressure, heat, and hot liquid acting on the rocks
Where volcanoes have or do exist
Deep within the earth – pressure, heat and hot liquid
OTHER
Soft, layered, may contain fossils crystalline, glossy, coarsegrained hard, may contain bands or layers, may contain crystals