The appearance of these rocks depends are the nature of these grains and the materials they are made of
MINERALS: Building blocks of rocks which are pure, naturally occurring solid material
You can have rocks made of 1 mineral (ex. limestone) or rocks made of 2 or more minerals (ex. granite) Of the minerals found in the Earth's crust the most abundant are:
Calcite
Quartz
Feldspar
Mica
Hornblende
The Rock Cycle
The three main classes of rock are:
Sedimentary
Metamorphic
Igneous
The differences between the classes of rock is how they are formed.
SEDIMENTARY ROCKS :
Formed from particles of sand, shells, pebbles, and other fragments of material.
Gradually, the sediment accumulates in layers and over a long period of time hardens into rock.
METAMORPHIC ROCKS:
Formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure.
Often have ribbon like layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface.
IGNEOUS ROCKS :
Formed when magma (molten rock deep within the earth) cools and hardens
When lava (magma on the surface of the Earth) cools very quickly gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.
May also cool and form a glassy like rock
Mineral Properties
1. Color 2. Lustre - How light interacts with the surface of the rock 3. Streak - Color of the powder left behind by dragging the rock over a surface 4. Cleavage - Cleavage describes how a mineral breaks into flat surfaces 5. Fracture - The shape and texture of the surface formed when a mineral is fractured 6. Hardness - The resistance which a smooth surface offers to abrasion (How easily a rock is scratched)
IN 1812 THE MOHS SCALE OF MINERAL HARDNESS WAS DEVISED BY THE GERMAN MINERALOGIST FREDERICH MOHS (1773-1839), WHO SELECTED THE TEN MINERALS BECAUSE THEY WERE COMMON OR READILY AVAILABLE.
This scale is a chart of relative hardness of the various minerals ( 1 - softest to 10 - hardest)