Week 2 Flashcards
defining characteristics of a mineral
1) naturally occurring
2) solid
3) inorganic (non-living)
4) definite chemical composition
5) ordered internal structure (crystalline)
Aggregate
implies that minerals are joined in such a way that the properties of each minerals are retained
how many elements are there
118, and 90 naturally occuring
Atom
the smallest part of matter that cannot chemically be split, an extremely small chemical that does the combining
why are atoms neutral
number of electrons = number of protons
covalent bonding
the sharing of an electron pair between two atoms
ionic bonding
the electrostatic force of attraction between a positively charged metal ion and a negatively charged non-metal ion
metallic bonding
Occurs in metals in pure, native form (e.g copper, gold, and silver)… Nuclei of metal atoms “float” in a sea of electrons. This free migration of electrons accounts for strong ability of metals to conduct electricity and the ease with which metals are shaped
intermolecular bonding
these bonds are very weak, produced by slight charge imbalances (“van der Waals” forces)
Crystal Form/Habit
Arrangement patterns of atoms within minerals are displayed in their external crystal form. The packing arrangement of atoms within any given mineral result in a characteristic geometry of crystal faces.
Cleavage
When a mineral breaks along well-defined planes. A mineral will preferentially break along planes of weaker bonding within the crystal structure
Fracture
Some minerals do not have a distinct cleavage due to more uniform bond strengths throughout the crystal structure (no distinct planes of weakness).
For example, broken surfaces of quartz are scoop-shaped. The curved surfaces look like the interior of a seashell, so is called conchoidal fracture.
Hardness
Measure of the resistance of minerals to being scratched. The hardness of a mineral reflects the overall strength of bonding within its crystal structure. Hardness is measured in units of Mohs scale of hardness.
Specific Gravity
A number representing the ratio of the weight of a mineral to the weight of an equal volume of water
Diaphaneity
Ability to transmit life. Can be transparent, translucent or opaque
Lusture
the appearance or quality of light reflected from the surface of a mineral
Metallic Lusture
the appearance of metal
EX. gold and pyrite
Non-metallic Lusture
not having the appearance of metal
EX. fluorite, calcite and tourmaline
Colour
primarily manifests the chemical content of a mineral. Also relates to the charges among ions within the mineral
Amethyst Quartz Colour
This “yellow” range of wavelengths of white light is absorbed. So we see wavelengths of purple, which is the complimentary colour on the colour wheel
Streak
Another way of identifying some minerals is to powder them. We do this by rubbing the mineral specimen against an unglazed porcelain plate called a streak plate
EX. Hematite (iron oxide) is redish brown
Gemstone beauty
Beauty of a gem is usually based on: colour, lustre, transparency, or unusual optical properties
The four C’s of gemstones quality
carat weight, colour, clarity and cut
Durability
the resistance of the gemstone damage and dependent upon physical properties, such as hardness and tenacity.
Tenacity
the resistance to bending and breaking
Stability
Usually refers to the gem’s resistance to destruction by chemical factors. Can also refer to how well a gemstone retains its colour
Weight
The carat (ct) is the standard unit of weight used in the pricing of gemstones. Due to differences in the density/specific gravity of different gems, carat weight can be misleading:
EX. a one carat sapphire is much smaller than a one carat opal, and a one carat diamond is smaller than a one carat sapphire
Rarity
reflects the uniqueness of natural geological processes that form them
Demand
Value of certain gemstones fluctuate with trends in fashion
Corundum
Usually dull in colour, Ruby and sapphire are just unusually beautiful forms of it.
Specimens of corundum with exceptional clarity and colour are used as gemstones
Asterism
Star pattern of light in some sapphires and rubies, resulting from the presence of inclusions of the rutile (TiO2). Play of light usually forms a six-sided star
Three basic cuts used
1) Cabochon
2) Brilliant
3) Step
Cabochon Cut
Simple round- to oval-shaped dome, used principally in translucent and opaque gemstones with bold colours and intermediate hardness.
EX. turquoise and opal
Brilliant Cut
Accentuates a gemstone’s ability to transmit, reflect and disperse light. Principally developed for diamonds.
Can have up to 59 facets that are carefully angled to highlight a stone’s brilliance and light disperson
Step Cut
broad table-like facet with smaller and longer rectangular facets around its edges. This type of cut emphasizes the colour of stones with a low degree of light dispersion
Varient of Step Cut: Emerald Cut
Developed to reduce edge damage of emeralds and other brittle gems
