Rocks Flashcards
Why do minerals have a fixed composition?
Because they are single compounds.
What is the difference between a grain and a crystal?
Crystals are solids with regular shapes and flat surfaces which reflect light. Whereas grains are small and hard and round. Rounded grains do not interlock as well as crystals do so that’s why a lot of sedimentary rocks are porous.
What is physical weathering?
Physical weathering is where forces cause rocks to break up. There are two main methods:
By freezing and thawing of water
By the expansion and contraction of rocks
What is ‘the expansion and contraction of rocks’ ? (Exfoliation)
It’s when a rock expands when it gets hotter, and contracts when it gets cooler. If it happens repeatedly it causes them to break, this often happens in the desert, where it’s hot in the day and cold at night.
What’s chemical weathering?
Chemical weathering is where the rock undergoes chemical reactions with substances such as water. For example the mineral calcite (calcium carbonate) in limestone reacts with rainwater. Rainwater is slightly a acidic due to carbon dioxide from the air of dissolving in rain.
Other substances from the soil and decaying plant material also dissolve in rainwater once it has fallen and make it more acidic.
Acidic rain, is rain that is more acidic than normal due to air pollution.
What is biological weathering?
Biological weathering is where plants and animals cause the rock to break up.
For example, the roots of the plants can grow into the rocks and break them apart, and animals can damage rocks as they burrow into the ground.
The slower the rock cools down….
…the bigger the crystals.
The faster the rock cools down…
…the smaller the crystals.
Properties of sedimentary rock…
Has grains
Soft
The grains are cemented together
Has layers that can be seen
Properties of igneous rocks …
Hard
Has randomly arranged, interlocking crystals
Has no holes, so not porous
Made form molten rock underground
Properties of metamorphic rock…
Mostly hard
Made under high pressure/temperature conditions
Arranged in fine bands or layers
Have mineral crystals
Made from other rocks which are either igneous or sedimentary
Examples of sedimentary rock…
Chalk
Limestone
Sandstone
Examples of igneous rock….
Obsidian
Granite
Examples of metamorphic rock…
Marble (made from limestone, which is a sedimentary rock)
Slate ( made from shale)
