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Rocks and Minerals
Transcript of Rocks and Minerals
a particular chemical makeup and orderly arrangement of atoms Rocks are usually composed of two or more minerals Minerals form from magma or lava or through evaporation or precipitation Mineral formation clues include
size and how mineral crystals fit together Properties of Minerals Characteristics are used to identify minerals Solids materials with a repeating
pattern of atoms are called crystals Some minerals have cleavage - splitting into thin sheets Some minerals have fractures - breaking into rough edges Color or streak - the color of a powdered mineral
- helps identify minerals Luster describes how light reflects from a mineral's surface Mohs scale uses hardness to classify minerals
from 1 (softest) to 10 (hardest) Specific gravity - compares weight of mineral with
weight of an equal volume of water. Other properties of minerals include magnetism,
double refraction, taste or reactions with acids Common Minerals Most rock forming minerals are silicates or carbonates Rare minerals which can be cut and polished are gems Diamonds are produced under pressure beneath Earth's surface and brought to the surface by special volcanic eruptions. An ore contains enough useful mineral to be sold at a profit Ores must be processed to extract the mineral formed from melted rock that cools Extrusive igneous rocks form when melted rock cools on Earth's surfaces Intrusive igneous rocks form when melted rock cools beneath Earth's surface Dark-colored rocks are often extrusive rocks Rocks that contain iron, magnesium, or calcium are called basaltic Detrital rocks - made of grains from minerals or other rocks
that have been compressed- see page 269 Organic rocks - form from dead plants and animals that hve been compressed -if the rock is produced from layers of plants, it is called coal -if the rock is produced from organic sediment
in the ocean, it is usually classified as limestone Formed when existing rocks are heated or squeezed; the recrystallize and might change chemically -rocks that have visible layers or elongated mineral grains are called foliated rocks -rocks that do not have layers are called non-foliated Time, pressure, and heat, and events such as erosion and moving land masses, make new rocks out of old rocks The Rock Cycle Rocks change from one type to another over millions of years The rock cycle model, or diagram, shows each rock on a continuing journey A rock in any part of the cycle could become any other kind of rock Granite Basalt Gneiss Quartzite Coal usually not formed from plants or animals Dark colored often extrusive igneous rocks containing iron, magnesium, or calcium are called basaltic Lava is melted rock that reaches Earth's
surface and forms extrusive igneous rock
when it cools. Light-colored often intrusive igneous rocks containing
a high percentage of silica are called granitic Formed from melted rock that cools see page 266-267 Volcanoes can erupt, bringing a lava to Earth's surface Large cracks or fissures can allow lava to ooze out in a lava flow Magma is melted rock that does not reach Earth's surface Intrusive igneous rocks form as magma slowly cools under the surface of the Earth. Pyrite Amethyst Mohs Hardness Scale
A man named Friedrich Mohs knew that different minerals have different hardness! Soft minerals have low numbers. Hard minerals have high numbers.
Mohs scale number (mineral example)
6 (Orthoclase Feldspar)
Hardness of other common objects
You can figure out the hardness of a mineral! Try to scratch it with your fingernail. If your fingernail cannot scratch the mineral, you know it has a hardness of more than 2.5. If the mineral can't scratch glass, you know it has a hardness of less than 5.5. Crystal size is the main difference between intrusive and extrusive igneous rock Intrusive igneous rocks have LARGE crystals
-because it is under the Earth's surface and cools
more slowly allowing larger crystals to form. Extrusive Igneous rocks have SMALLER crystals
- because the lava cools quickly on the surface
of the earth before
large crystals have time to form Water, ice, gravity or wind can cause grains of minerals to move and be deposited in layers Sediment is peices of broken rock, shells, mineral grains, and other materials. Chemical rocks - form when mineral-rich water evaporates and from other chemical processes see page 270 Chalk is a kind of limestone made from the fossils of tiny animals and algae Living matter dies, piles up, and then is compressed into rock Chalk is a kind of limestome made from the fossils of tiny animals and algae