What is a rock? A rock is a naturally occurring solid substance that is normally made of minerals. Some rocks are made of only one mineral. Others are made of several minerals combined. By figuring out what minerals are in a rock and understanding how they are formed geologist place rocks into one of three groups: Igneous metamorphic and sedimentary .

What is a mineral? Minerals are the building blocks of rocks. Scientists have discovered over 3,000 types of minerals! A mineral is a natural, nonliving substance.

Properties of minerals Color: Color alone, cannot identify minerals. Many minerals have the same color. Quartz can be many different colors! Hardness: refers to a minerals ability to scratch another mineral or be scratched. The MOHS’ Scale shows the hardness of some common minerals. Each mineral has a number one - ten. Ten is the hardest kind.

Luster: refers to the way light bounces off the surface of a mineral Luster: refers to the way light bounces off the surface of a mineral. Some have a metallic, or shiny luster. Minerals with no shine at all have a dull luster. Streak: If you scratch a mineral along a white tile, it leaves behind a powder. A minerals streak is the color of that powder. The streak may be different from the color of a mineral’s surface!

Properties of minerals mica feldspar hematite pyrite color white, green, silver, or brown white, pink, gray, or smoky black gray or brown gold or brassy yellow luster pearly dull or glassy metallic or dull metallic streak white red green-black hardness 2 - 2.5 6-6.5 5-6

Igneous rocks can also form from lava above earth’s crust. Below earth’s surface are areas of melted rock called magma. When magma cools and hardens, igneous rocks form. Igneous rocks can also form from lava above earth’s crust. The texture of an igneous rock depends on how fast the magma cools to form the rock. The slower it takes to cool the more mineral grains will form. If it cools quickly, the rock will have a smoother, glassy texture. granite obsidian basalt

Sedimentary Rocks These layers are made of tiny pieces called sediments. Some sediments are formed from rocks or minerals. Others are bits of plants, shells, or other hard materials. Sedimentary rocks are formed from sediments that are pressed and cemented together. It can take millions of years for sediments to become rocks!

metamorphic Rocks When rocks are under extreme heat or pressure (like under earth’s surface!) their physical appearance can change. A metamorphic rock is a rock that is formed from other rocks by extreme heat and pressure. granite gneiss

Cycle The Rock