Chapter 2: Minerals

Van der Waals force

A weak force that occurs because electrons are not always distributed equally around all sides of a molecule which creates polar molecules which are then weakly attracted to each other.

What determines the COLOR of a mineral? Also what causes different colors of the same mineral to occur?

Atomic arrangement and composition determine how light passes through the crystal. Color variations happen when trace elements replace a few similar-sized and charged atoms(ions) of the more abundant elements in a crystal.

Metallic bonds

Formed when electrons roam freely among several atoms. Creates conductivity.

What are ions and what types are there?

Ions are atoms in which the number of elections does not match the number of protons resulting in either a positive or negatively charged ion. Positively charged ions are called Cations (less electrons) and negatively charged ions are called anions (more electrons).

What determines the LUSTER of a mineral?

Luster depends on the smoothness of the mineral surface at the atomic scale, which, in turn, depends on how mobile electrons are within the crystal.

Silicates

Minerals that contain silicon and oxygen.

Mineral

Naturally occurring inorganic solid with a definite, only slightly variable chemical composition and and ordered atomic structure.

What are the two most common elements in the crust?

Oxygen and silicon

Crystal Faces

Smooth, flat surfaces with regular geometric outlines.

Rock-forming Minerals

The abundant minerals at the surface of the earth that form rocks.

Streak

The color of the residue produced by scratching a mineral on a non-glazed porcelain plate. Different specimens of the same mineral may vary in color but the streak color is always the same.

Why is STREAK important?

The fine-grained nature of the powdered residue results in a more reliable observed color than the whole crystal.

Cleavage

The flat smooth planes along which some minerals break. Also refers to the shape of the fragments when you break a mineral with cleavage.

Density

The measure of the mass of a material divided by its volume.

Feldspars

The most common group of minerals in the crust. They are the result of aluminum-for-silicon substitution.

Fracture

The surface of a mineral that breaks along unpredictable and irregular planes.

What determines crystal structure?

The way in which the atoms of a mineral are arranged and this is due to bonding.

What determines the shape of the CRYSTAL FACE of a mineral?

crystal faces reflect the atomic arrangement of atoms within the crystal structure and produce geometric shapes during growth unless the crystal grows against another crystal.

Ionic bond

forms as a result of the attraction between negative and positive ions and occurs when electrons are transferred from one atom to another to satisfy valence shells.

Ore Minerals

minerals that are not pure but contain useful metallic elements that must be extracted for use.

Hardness

the measure of the resistance of a mineral surface to scratching.

Luster

used to describe how mineral surfaces reflect light. (Ex:Dull/Shiny)

Covalent bond

when two or more atoms share electrons to simultaneously fill the outer electron shell of the atoms.

What determines the CLEAVAGE of a mineral?

Cleavage forms along regularly spaced internal planes where bonds are weakest in minerals.

What determines the DENSITY of a mineral?

Density depends on the types of atoms and how the atoms are arranged in the crystal structure. The heavier atoms are and the more tightly packed they are, the higher the density of the mineral.

Mohs hardness scale

Describes mineral hardness on a scale of 1-10. Relative scale; not absolute. More of a field tool to determine the relative hardness of a mineral compared to other minerals.

What are the principal properties used to identify and describe minerals? (7)

1.color 2.luster 3.streak 4.hardness 5.cleavage/fracture 6.density 7.external crystal form