Earth Science - Chapter 2

Minerals

Atom

smallest particle that exists as an element

Atomic number

the number of protons in the nucleus of an atom

Atomic weight

the average of the atom masses of the isotope for a given element

Cleavage

the tendency of a mineral to break along planes of weak bonding resulting in smooth, flat surfaces

Colour

a phenomenon of light by which otherwise identicle objects can be differentiated

Compound

a substance formed by the chemcial combination of two or more elements in definite proportions and usually have properties different from those of its consitituent elements

Covalent bond

a chemical bond by the sharing of electrons between atoms, typically nonmetals, resulting in a stable balance of attractive and repulsive forces.

Crystal habit

the external appearance of a mineral as determined by its internal arrangement of atoms

Dark silicate/Ferromagnesian silicate

silicate minerals that contain ions or iron or magnesium (or both) in their structure, they are dark in colour and have a higher specific gravity than nonferromagnesian silicates

Electron

a negatively charged subatomic particle that has negligible mass and is found outside an atoms nucleus

Energy levels

the spherical shaped, negatively charged zones that surround the nucleus of an atom

Fracture

a structure break, crack, or separation within a geological formation that divides a rock into two or more pieces because of stress

Hardness

a minerals resistance to scratching and abrasion

Ion

an atom or molecule that possesses an electrical charge

Ion bond

a chemical bond between two oppositely charged ions formed by the transfer of valence electrons from one atom to the other

Light silicate/Nonferromagnesian silicates

silicate mineral that lacks iron or magnesium, they are generally lighter in colour and have lower specific gravities than dark silicates

Lustre

the appearance or quality of light reflected from the surface of a mineral

Mineral

naturally occuring, inorganic crystalline solid material with a specific chemical composition

Mineralogy

the study of minerals

Mohs scale

a series of 10 minerals used as a standard in determining hardness

Neutron

a subatomic particle found in the nucleus of an atom, the neutron is electrically neutral, with a mass approximately equal to that of a proton

Nucleus

the small, heavy core of an atom that contains all of its positive charge and most of its mass

Polymorphs

two or more minerals that have the same chemical composition but different crystalline structures, they are exemplified by the diamond and graphite forms of carbon

Proton

a positively charged subatomic particle found in the nucleus of an atom

Rock

a consolidated mixture of minerals

Shells

the spherically shaped, negatively charged zones that surround the nucleus of an atom

Silicate

any of numerous minerals that have the silicon-oxygen tertrahedron as their basic structure

Silicon-oxygen tetrahedral

a pryamid-shaped structure composed of four oxygen atoms surrounding a silicon atom that consititutes the basic building block of silicate minerals

Specific gravity

the ratio of a substances weight to the weight of an equal volume of water

Streak

the colour of a mineral in powder form

Valence electron

the electrons involved in the bonding process, occupyinh the highest energy level/shell of an atom

Intermolecular bonding

relatively weak electrostatic forces of attraction between neighbouring molecules

Metallic bonding

strong electrostatic attraction between postively charged metals ions and a shared “sea” of delocalized electrons, also tend to be weak

Non-silicate minerals (sulphides)

Pyrite, Galena, Sphalerite

Non-silicate minerals (carbonates)

calcite

Non-silicate minerals (halides)

halite, fluorite

Non-silicate minerals (phosphates)

Apatite

Non-silicate minerals (oxides/hydroxides)

Hematite, Magnetite, Goethite

Colour

Primarily manifests the chemical content of a mineral, colour can be a very diagnostic property, but it can also be very misleading

example: pyrite (iron sulfide - “fools gold”) brassy colour

Streak

another way to identify some minerals is to powder them, rubbing the mineral specimen against an unglazed porcelain plate called a streak plate

examples: hematite (iron oxide) reddish-brown streak

Crystal habit

arrangement patterns of atoms within minerals are manifest in their external geometric shape, packing arrangement of atoms within any given mineral results in a characterstic geometry of crystal faces

example: halite (sodium chloride or NaCl) has a cubic form

Diapheneity

Ability to transmit light

Transparent - light enters and exits in relatively undisturbed fashion (like through clear glass)

Translucent - light enters and exits the mineral, but in a rather scattered fashion (like through milk)

Opaque - light cannot penetrate the surface of the mineral (like a piece of metal)

Lustre

Ability of the mineral to reflect light.

Metallic lustre - reflect light like a polished metal

Non-metallic lustre - most minerals have some type of non-metallic lustre (examples: vitreous (like glass), pearly, greasy, earthy)

Types of cleavage and their direction

Basal - 1 direction

Prismatic - 2 directions, important to state whether at right angle or not

Cubic - 3 directions at right angle

Rhombohedral - 3 directions, not at right angles

Octahedral - 4 directions