Minerals

What are minerals?

• A mineral is a solid, natural material made from nonliving substances in the ground.

• Minerals are made up of elements. An element is a pure substance that cannot be broken down into a simpler substance.

• Examples of elements are gold, aluminum, oxygen, hydrogen, and iron.

• Some minerals are made up of a single element while others are made of two or more.

• Minerals are the building blocks of rocks.

What are the properties of minerals?

Luster

• Luster is the way a mineral reflects light from its surface.

• There are two general kinds of luster.• Minerals with a metallic luster look shiny,

while minerals with a nonmetallic luster look duller.

• Minerals with a nonmetallic luster may look waxy, pearly, earthy, oily, or silky.

Color• Usually, we notice the color of a mineral

first. • Some minerals are easily identified by

color because they are never any other color. For example, malachite is always green.

• Keep in mind, however, that color by itself isn't enough to identify a mineral.

• For example, quartz in its purest form is colorless and clear as glass.

• Quartz with traces of iron becomes violet (amethyst).

• With traces of manganese, it turns pink (rose quartz).

• If quartz is exposed to radiation, it turns brown (smoky quartz).

Streak

• When a mineral is rubbed firmly across an unglazed tile of white porcelain (a streak plate), it leaves a line of powder. This is called the streak.

• The color of the streak is always the same, whether or not the mineral has impurities.

• For example, quartz leaves a white streak, whether it's violet (amethyst), pink (rose quartz), or brown (smoky quartz).

Hardness

• Hardness is a measure of how well a mineral resists scratching.

• A hard mineral resists scratching better than a softer mineral.

• On Mohs’ hardness scale, minerals are ranked from 1, which is the softest, to 10, which is the hardest.

• By scratching an unknown mineral with materials that have a known hardness, you can find the hardness of an unknown mineral.

Transparency

• Transparency describes how well light passes through a mineral sample.

• There are three degrees of transparency: transparent, translucent, and opaque.

• You can see objects through a transparent mineral.

• You can see light, but no objects through a translucent mineral.

• You can't see anything through an opaque mineral.

Cleavage

• When a mineral is broken, it breaks along planes of weakness that are part of its crystalline structure. These breaks are cleavages.

• The appearance of the surfaces of the mineral can help identify it.

• When the surfaces are smooth, the property that it has is cleavage.

• Cleavage is described by the number of planes along which the mineral breaks.

Fracture

• Fracture is the property a mineral shows when it has uneven or rough surfaces.

• Not all minerals cleave easily. Some fracture instead.

• Unlike cleavages, which are usually clean, flat breaks, fractures can be smoothly curved, irregular, jagged or splintery.

Crystal Form

• Minerals grow in specific shapes, and usually crystallize into one of six crystal systems.

• The axes of the crystal, the angles at which the axes intersect, and the degree of symmetry define each system.

• Different minerals have different crystal shapes.

Gems

• Some minerals, such as emeralds, are also called gems.

• A gem is a mineral that is rare, beautiful, usually transparent, and glitters or shines in light.

• While gems are often rough and uneven in their natural form, they can be cut into shapes to show their color and remove their flaws.

• After being cut and polished, many gems are used in jewelry.

Mineral Samples

• Pink – Feldspar

• White – Quartz

• Rough Black – Hornblende

• Smooth and Silvery - Mica