What are Rocks? What are Minerals?
What are Rocks?
Rocks are made up of grains of one or more minerals. Rocks form the Earth’s crust and include the surface forms we see every day.
Sedimentary Rocks cover about three-quarters of the earth’s surface. Sedimentary rocks form through the erosion, movement, and redeposit of minerals. Over time eroded rocks and minerals build-up and compress together over millions of years to form rock. Most sedimentary rocks form in layers and many contain fossils.
Examples:
limestone
sandstone
shale
conglomerate
Igneous Rocks form from magma (molten rock) that comes from deep inside the earth. Magma that cools below the earth’s surface is called intrusive rock. Magma that cools above the surface such as lava from a volcano is called extrusive rock. Metal ores and gemstones often form in the veins and fissures of igneous rock. Quartz forms an important part of most igneous rock.
Examples:
granite (intrusive)
pegmatite (intrusive)
obsidian (extrusive)
basalt (extrusive)
Metamorphic Rocks are rocks that have undergone change. Any type of rock can be metamorphosed—igneous, sedimentary, and other metamorphic rocks. Metamorphism occurs under great heat, pressure and/or permeation of other minerals such as liquid or gas.
Examples:
shale turns to slate
limestone turns to marble
sandstone turns to quartzite
granite turns to gneiss (nice)
What are Minerals?
Calcite is the most common and wide spread of the carbonate minerals. Calcite occurs in a variety of crystal forms.
Quartz is the most common mineral in the earth’s crust. In its purest form it is called silica which is the basis of many rocks and minerals. Quartz comes in an abundant variety of colors and crystal forms.
