Minerals Flashcards
About how many known minerals are there?
~3500
How many minerals are reasonably common?
~200
How many minerals account for most of the earth’s crust?
~20
What class of mineral makes up 94% of the crust?
silicate minerals
What are minerals in the crust limited by?
the elements available and silicate mineral structure
What 5 properties must a substance meet to be considered a mineral?
naturally-occurring, inorganic, crystalline solid, definite chemical composition, characteristic physical properties
What are a mineral’s physical properties determined by?
chemical composition and crystal structure
What are ionic bonds?
electromagnetic attraction
What mineral contains ionic bonds?
halite (table salt)
Why are ionic bonds brittle?
when cracked, negative and positive ions repel and push each other away
What type of bond involves metal ions “floating” in an electron sea?
metallic bonds
How do metallic bonds behave?
plastic
What are covalent bonds?
sharing of electrons
What is the composition of most silicate bonds?
50:50 covalent:ionic
What does the composition of silicate bonds indicate about their behaviour?
behave elastically but break in brittle manner
How do covalent bonds behave?
elastic and flexible
What is crystal structure?
arrangement of atoms in a regularly repeating, orderly pattern
What is a crystal?
homogeneous solid bounded by naturally-formed planar surfaces
What are planar surfaces?
external expression of internal ordering of atoms
What does the internal ordering of atoms in a crystal result in?
specific angular relationships
What bonds determine crystal structure?
strongest bonds
What bonds determine crystal strength?
weakest bonds
What are 5 ways in which minerals can form?
solidification of a melt, precipitation from solution, solid state diffusion, biomineralization, precipitation from gas
What is an anhedral?
mineral without well-formed crystal faces
How do anhedrals often form?
growth in a confined space
What is a euhedral crystal?
well-formed crystal faces (uninhibited growth)
What 8 elements make up 99% of the Earth’s crust (by weight)?
O, Si, Al, Fe, Mg, Ca, Na, K
Does carbon play an important role in the crust?
no
Why do so many minerals contain oxygen?
out of the 8 common minerals, only oxygen forms a negative ion, which is needed to make compounds electrostatically stable
What 2 other elements behave similarly to calcium?
sodium and potassium
What element behaves similarly to iron?
magnesium
What elements form a silicate ion?
silicon and oxygen (SiO4)
What are the 2 most abundant elements?
silicon and oxygen
How strong is the structure of one silicate?
strong bonds but electrically unstable
What shape do silicate ions form?
tetrahedral
Why is a silicate tetrahedra electrically unstable?
negative 4 charge
What are two ways in which silicates balance their strong negative charge?
bonding with positive ions or polymerizing by sharing electrons (between oxygens)
What mineral is an example of isolated silicate tetrahedra?
olivine
How do silicates form single chains?
share one oxygen atom
What silicate structure does pyroxene have?
single chains
What silicate structures can be formed by sharing oxygens?
single chains, double chains, sheet silicates, and framework silicates
What is an example of a mineral with double chain silicates?
amphibole
What mineral contains silicate sheets?
mica
What silicate structure do feldspar and quartz have?
frameworks
How are framework silicates formed?
all 4 oxygens are shared (3-D structure)
How many oxygen atoms are shared to make a silicate sheet?
three
What cleavage do silicate sheets form in minerals?
strong cleavage in 1 direction
What are the mechanical and chemical properties of quartz?
mechanically durable (strong 3-D covalent array) and chemically stable
Why is quartz used for glass?
it’s inert and clear
What is the most abundant “rock-forming” mineral group?
feldspar
What are the two main types of feldspars?
orthoclase (K) and plagioclase (Na or Ca)
How do feldspar’s chemical properties relate to those of quartz?
chemically inert but less so than quartz
What minerals are part of the mineral assemblage in basalt?
olivine, pyroxene, and plagioclase
What colour is olivine?
olive green
What two possible ions can bind to silicate to form olivine?
Mg or Fe
What silicate chemistry is found in hornblende (amphibole-group mineral)?
double-chain
What are the parts of the mineral assemblage in andesite?
K-feldspar, plagioclase, amphiboles, biotite
What colour is hornblende?
very black
What mineral is found in shells and limestone?
calcite
What is the chemical formula for calcite?
CaCO3
What kind of cleavage does calcite have?
rhombohedral (skewed boxes)
What mineral exhibits double refraction?
calcite
In what is calcite soluble?
dilute acid
Why is calcite easy to precipitate out of solution?
it has a very narrow solubility
What is the hardness of gypsum (qualitatively)
soft - can scratch with fingernail
What is gypsum soluble in?
water
What is the mineral with the formula CaSO3.2H2O?
gypsum
What is the mineral table salt?
halite
What shape of crystal does halite form?
cubic
What mineral is an important source of acid drainage and how?
pyrite (oxidizes easily; forms sulfuric acid in solution)
What mineral is known as “fool’s gold”?
pyrite
What is pyrite’s chemical formula?
FeS2
What mineral commonly “replaces” more soluble minearls?
pyrite
What is the most abundant sulphide mineral?
pyrite
What is an important part of most iron ore?
magnetite
What mineral has the formula Fe3O4?
magnetite
What colour/streak is hematite?
reddish orange
What is the mineral and its formula that forms rust?
hematite; Fe2O3
What minerals make up granite?
quartz, K-feldspar, plagioclase feldspar, mica (biotite and muscovite)
What is the chemical formula for quartz?
SiO2
What are some physical properties used to describe and identify minerals?
colour, lustre, streak, harness, habit, fracture, cleavage, density, taste, odor, magnetism, radioactivity…
From what does colour result?
variable absorption of white light
Why is colour not a reliable identifier for most mineral?
it’s variable due to impurities
What is lustre?
appearance in reflected light - how light reflects off an object
What are the two main categories of lustre?
metallic and non-metallic
What is the lustre of silicates?
non-metallic
What minerals have a metallic lustre?
metals and sulphides
What is streak?
colour of powdered solid
What physical property is more reliable than colour?
streak
What types of minerals is streak most useful for?
sulphides and oxides (metallic minerals)
What are the two terms to describe how a substance breaks?
cleavage and fracture
What is the difference betwen cleavage and fracturing?
fracturing occurs on non-planar surfaces while cleavage breaks along parallel planes, resulting in repeating parallel surfaces
What does Mohs’ scale of relative hardness measure and how?
measures mechanical strength by “scratchability”
What are the 9 minerals used in Mohs’ scale?
- talc
- gypsum
- calcite
- fluorite
- apatite
- feldspar
- quartz
- topaz
- corundum
- diamond
Is Mohs’ hardness scale linear?
no
What measure of density is commonly used in geology?
specific gravity
What is specific gravity?
density compared to water
Why does gold panning work?
gold has a much higher specific gravity than other common minerals in the water
