Essential (vitamins and) minerals What makes up the earth?

What is a mineral? Scientists define a mineral as a “natural, inorganic, crystalline solid”. An inorganic substance is one that is not made up of the remains of living things. Rocks are combinations of the various minerals of the earth. Using this definition, why is coal not a mineral?

Questions to ask Does the material occur naturally? Brass is an alloy of zinc and copper, and therefore is not a mineral. Is it made up of the remains of living things? Is it a solid in its natural state? Does it have a definite chemical composition?

Silicate vs. non-silicate Minerals that contain the elements silicon (Si) and oxygen (O) are considered silicate minerals. They make up 96% of the earth’s minerals. Examples include quartz, hornblende, muscovite, biotite, and feldspar (which is the most common).

Non-silicates Minerals such as galena, pyrite, and fluorite do not contain Si or O. 4% of the earth’s minerals are non-silicates. Silver, by itself, is a non-silicate, but is often found as a compound with other common minerals.

Rocks vs. minerals While a mineral is considered as part of the earth’s composition, a rock is a collection of minerals that are bound together physically or chemically. Rocks undergo the rock cycle and can be igneous, sedimentary, or metamorphic. Most rocks have a definite chemical composition while others do not.

Igneous rock characteristics Igneous rocks are either intrusive or extrusive. Intrusive rocks cool slowly in the earth. Extrusive rocks cool quickly on the surface. Some rocks can begin cooling slowly, but reach the surface and then cool quickly – this is called a porphyry.

Igneous rock composition You may recall that lava can be either mafic or felsic. Felsic lava creates rocks that are high in the element silicon, such as granite. In fact, all rocks created from felsic lava are in the granite family. Mafic lava creates rocks rich in iron, called the basalt family.

Composition continued A third family called the diorite family is a combination of felsic and mafic lava. Diorite is typically an intrusive formation forming at plate oceanic-continental plate boundaries.

Igneous rock intrusions Batholiths are large underground collections of igneous rock, usually bigger than 100 km^2. Stock is similar but smaller than 100 km^2. Laccoliths are hill-shaped deposits in the crust that push the land up beneath it.

Intrusions continued A sill is a magma formation that is parallel to the rock layers in the crust. A dike is usually a pathway for magma to reach the surface, and cuts vertically through rock layers.

Igneous rock extrusions A volcano is the most common extrusion. A volcanic neck is the vent of an eroded volcano. A lava plateau develops from previous volcanic eruptions and is flattened out over time by weathering and erosion.

Pictures Shiprock – a volcanic neck formation Batholith formations on the surface. Salisbury crags – a sill exposed during the ice age.