Earthsci Midterm

• What are metamorphic rocks made of?

  Mineral crystals that looks flattened or stretched
• What are sedimentary rocks made of?

  Particles of pre-existing rocks
• What are igneous rocks made of?

  Randomly interlocking mineral crystals
• What are the 3 basic types of rocks?

  Igneous, sedimentary, metamorphic
• What is an emerald cut?

  - Step cut without the corners

  - Developed to reduce edge damage of emeralds and other gems with brittle tenacity
• What is a step/trap cut?

  - Table-like central facet surrounded by smaller and longer rectangular facets around edges

  - Main facet can range in shape

  - Emphasizes colour of stones with low degree of light dispersion
• What is a brilliant cut?

  - Accentuates gemstones ability to transmit, reflect, disperse light

  - Allows largest possible number of gems to be cut from a sample with minimal waste
• What is a cabochon cut?

  - Simple round/oval shaped

  - Used mostly in translucent and opaque gemstones with bold colours and low/intermediate hardness

  - Used to show off properties like asterism
• What are the 3 basic ways to cut a gemstone?

  Cabochon, brilliant, step/trap
• What is an aquamarine?

  Aquamarine is a blue variety of beryl
• What is an emerald?

  Emerald is a brilliant green version of beryl
• What is the typical range of points that an asterism can have?

  6-12
• What is an asterism?

  Star pattern within the corundum crystal
• When is a sapphire classified as a sapphire?

  When rubies exhibit any colour other than red
• When is a Ruby classified as a Ruby?

  When corundum contains enough chromium it exhibits a deep red colour
• What does the rarity of a gemstone reflect?

  Exceptional nature of natural geological processes that form the gem
• How many grams is a carat?

  0.2
• What is a carat?

  Standard measure of weight in pricing of gemstones
• What defines the stability of a gemstone?

  Gem's resistance to destruction by chemical factors
• What defines the durability of a gemstone?

  The resistance of a gemstone to damage
• What are the 4 C's?

  - Colour

  - Clarity

  - Cut

  - Carat weight
• What is the standard of gemstone beauty based on?

  - Colour

  - Lustre

  - Transparency

  - Cut
• What are the 3 valuable qualities of gemstones?

  Beauty, durability, stability
• What are the 2 categories of gemstones?

  - Precious

  - Semiprecious
• What is a gem?

  A gemstone that has been cut to accentuate its beauty
• What is a gemstone?

  Ornamental stones for personal adornment
• What is gemmology?

  The study of gems
• What is streaking?

  Identifying a mineral by rubbing a mineral specimen against an unglazed porcelain plate/streak plate
• How does colour manifest in a mineral?

  Chemical content of a material
• What is lustre?

  Ability to reflect light from its surface
• What can't opaque minerals do?

  Let light through
• What can translucent minerals do?

  Scatters light so you can't see through it clearly
• What can transparent minerals do?

  Transmit light undisturbed
• What does hardness reflect?

  - Overall strength with bonding to crystal structure

  - Minerals with high hardnesses can cut softer minerals

  - Minerals of equal hardnesses can cut each other
• What is a fracture?

  Appearance of a broken surface that is not cleavage
• What is basal cleavage?

  Cleavage in one direction
• When does cleavage occur?

  When minerals have bonds of different strengths

  Ex. Weaker bonded minerals are easier to break
• What is cleavage?

  - Breaking of a mineral along flat and well-defined planes

  - Manifestation of internal structure of mineral crystals
• What is metallic bonding?

  - Occurs only in pure or native metals

  - Nuclei of metal float in a sea of electrons

  - Electrons constantly migrate among ions of substance
• What is graphite made out of?

  Covalently bonded carbon