Chapter 3: Minerals Slide Set 9 Flashcards
What is the geologist’s definition of a mineral?
A naturally occurring solid, formed by geologic processes, that has a crystalline structure and definable chemical composition
- Naturally occurring
- Formed geologically
- Solid
- Crystalline structure
- Definite chemical composition
- Inorganic (few exceptions)
How are minerals created?
- true mineral is created by natural processes.
- Humans can recreate natural processes to make
minerals. - These are called synthetic minerals.
What are the geologic processes that form minerals?
- Freezing from a melt
- Precipitation from a dissolved state in water
- Chemical reactions at high pressures and temperatures
Living organisms can create minerals. What are those called? Give examples
Called biogenic minerals to emphasize this special origin
- Vertebrate bones (apatite)
- Oyster, mussel, and clam shells (aragonite)
- Other skeletal types
- Our own tooth enamel (apatite)
What is the state of matter of minerals?
They are solid.
- A state of matter that can maintain its shape indefinitely
- Minerals are solids, not liquids or gases.
True/False
Minerals can be solid, liquid and gas
False
only solids
What is the structure of minerals?
They have a crystalline structure.
Atoms in a mineral are arranged in a specific order. This atomic pattern is called a _______
crystal lattice
A solid with disordered atoms is called a _____.
glass
True/False
Glasses are minerals
False
Lacking crystalline structure, glasses are not minerals.
True/False
Minerals can be defined by a chemical formula.
True
Give examples for simple and complex minerals
Simple
- Ice—H2O
- Calcite—CaCO3
- Quartz—SiO2
Complex
- Biotite—K(Mg,Fe)3(AlSi3O10)(OH)2
- Hornblende—Ca2(Fe2+,Mg)(Al,Fe3+)(Si7Al)O22(OH,F)2
Can minerals be organic? What elements can they contain? Explain
They are mostly inorganic. - Organic compounds - Contain carbon–hydrogen bonds - Other elements may be present. (Oxygen Nitrogen Sulfur) - Common products of living organisms - Most minerals are NOT organic.
Why is studying minerals important?
- Minerals are the building blocks of the planet.
- Minerals make up all of the rocks and sediments on
Earth. - Understanding Earth requires understanding minerals.
- Minerals are important to humans.
- Industrial minerals—raw materials for manufacturing
- Ore minerals—sources of valuable metals
- Gem minerals—attract human passions
What is a crystal?
- A single, continuous piece of crystalline solid
- Typically bounded by flat surfaces (crystal faces)
- Crystal faces grow naturally as the mineral forms.
- The same mineral has the same crystal faces.
- Adjacent faces occur at the same angle to one another.
- Faces and angles reflect crystalline structure.
What is an X-ray diffraction?
X-ray beam splits into numerous smaller beams. Interference of waves of different beams produces a diffraction pattern on a screen or film. The pattern indicates the spacing and arrangement of atoms
Physical properties of a crystal (hardness, shape) depend upon:
- Identity of atoms
- Arrangement of atoms.
- Nature of atomic bonds
What is the structure of a diamond like?
In diamonds, each atom bonds to four neighbors arranged in the form of a tetrahedron. The bonds between the carbon atoms are covalent, meaning that they share electrons, i.e., their electron clouds overlap and, as a result, the bonds are very strong. … Hardest mineral known to man.
Which one is a stronger bond? Covalent or Ionic?
Covalent
What is the structure of a graphite like?
Covalent bonding of 3 carbon atoms within each sheet within the sheets carbon atoms share their electrons with three other carbon atoms through covalent bonding
Where are diamonds found?
Diamonds originate under extremely high pressure.
- ~150 km deep—in the upper mantle
- Pure carbon is compressed into the diamond structure.
- Rifting causes deep-mantle rock to move upward.
How do mineral crystals form? What are the possible processes? Give example
- Mineral crystals form when a melt solidifies. Quick cooling results in tiny crystals; slow cooling creates large crystals.
- New crystals can form from an aqueous solution when dissolved solids become saturated.
A common way for this to happen is by evaporation of water. - Mineral crystals can sometimes precipitate directly from a gas.
- As rocks are buried to great depths, new crystals form.
- Biomineralization forms new crystals. (teeth)
How are minerals formed?
- Outward crystal growth fills available space.
- Resulting crystal shape is governed by surroundings.
The open space is where the ____ faces grow
good crystal faces grow
The confined space is where there is _____ faces
no crystal faces
Mineral growth is often restricted by _______.
lack of space
What does anhedral mineral mean?
grown in tight space, no crystal faces
What does euhedral mineral mean?
grown in an open cavity, good crystal faces
Which one is more common anhedral or euhedral?
Anhedral crystals are much more prevalent.
Euhedral crystals grow into the open space in a ______
geode
Minerals can be destroyed by:
- Melting—heat breaks the bonds holding atoms together
- Dissolving—solvents (mostly water) break atomic bonds
- Chemical reaction—reactive materials break bonds
When we say that a material is crystalline we mean that internally . . .
A. atoms are distributed in an orderly arrangement.
B. atoms and/or clusters of atoms are arranged randomly. C. atoms are arranged strictly in microscopic cubes.
D. the material occurs only in crystals with nicely formed
crystal faces.
D
The chemical formula of quartz is SiO2. This means that if you analyze a piece of quartz, you will find that . . .
A. the piece contains equal parts of sodium and chlorine.
B. the piece contains one silicon atom for every two
oxygen atoms.
C. the piece contains a random mixture of silicon and
oxygen atoms.
D. the piece contains a great variety of different elements.
B
What are the common physical properties of minerals?
- Color
- Streak
- Luster
- Hardness
- Specific gravity
- Crystal habit
- Fracture or cleavage
How is the color of a mineral analyzed and classified?
- The part of visible light that is not absorbed by a mineral
- Diagnostic for some minerals
- Malachite is a distinctive green.
- Some minerals exhibit a broad color range.
- Quartz (clear, white, yellow, pink, purple, gray, etc.)
- Color varieties often reflect trace impurities.
How is the color interpreted if a mineral is lets say green?
A mineral absorbs certain colors/wavelengths, so the color you see when looking at it is the wavelength it does not absorb.
So green is the color that the mineral does not absorb
What is the streak of a mineral? How is it interpreted?
- Color of a powder produced by crushing a mineral
- Obtained by scraping a mineral on unglazed porcelain
- Streak color is less variable than crystal color.
What is the luster of a mineral? How is it interpreted?
The way a mineral surface scatters light
What are the subdivisions of luster?
Metallic—looks like a metal
Nonmetallic
- Silky
- Glassy
- Satiny
- Resinous
- Pearly
- Earthy
What is the hardness of a mineral? How is it interpreted?
- Scratching resistance of a mineral
- Derives from the strength of atomic bonds
- Hardness compared to the Mohs scale for hardness. (graphite lowest, diamond highest)
What is the specific gravity of a mineral? How is it interpreted? Give examples
- Represents the density of a mineral
- Mineral weight over the weight of an equal water volume
- Specific gravity is heft—how heavy it feels.
- Galena—heavy (SG 7.60)
- Quartz—light (SG 2.65)
- Galena feels heavier than quartz.
What is the crystal habit of a mineral? How is it interpreted?
- single crystal with well-formed faces, or
- An aggregate of many well-formed crystals
- Arrangement of faces reflects internal atomic structure
- Records variation in directional growth rates
What are the possible variations in directional growth rates? Explain each
- Blocky or equant—equal growth rate in three dimensions
- Bladed—shaped like a knife blade
- Needle-like—rapid growth in one dimension, slow in
others
What is the habit?
The habit is the shape of a single crystal with well-formed (euhedral) crystal faces, a macroscopic reflection of the internal arrangement of atoms in the crystal
What is a cleavage?
- Cleavage is the tendency for a mineral to break along lattice planes with weaker atomic bonds
- Cleavage creates flat, shiny (reflective) surfaces that may occur in steps.
- Cleavage can be distinguished from crystal faces because it is throughgoing; faces are on external crystal surfaces only.
What are the possible directions of a cleavage?
- One direction
- Two directions at 90º
- Two directions NOT at 90º
- Three directions at 90
- Three directions NOT at 90º
Glass breaks with ______ fracture
conchoidal fracture
Can minerals that have no lattice planes cleave? Explain
Minerals that have no lattice planes of weakness— bonds equally strong in all directions—will fracture instead of cleave
What are Special Physical Properties that minerals can have?
- Effervescence—reactivity with acid (e.g., Calcite)
- Magnetism—magnetic attraction (e.g., Magnetite)
- Taste - halite tastes salty
- Smell - sulfur smells like rotten eggs
- Feel—tactile response
- Elasticity—response to bending
- Diaphaneity—relative transparency
- Piezoelectricity—electric charge when squeezed
- Pyroelectricity—electric charge when heated
- Refractive Index—degree of bending light
- Malleability—ability to be pounded into thin sheets
- Ductility—ability to be drawn into thin wires
- Sectility—ability to be shaved with a knife
What statement about the specific gravity of minerals is correct?
A. If a mineral has a specific gravity of 2, then a cubic
centimeter of the mineral weighs twice as much as a
cubic centimeter of water.
B. Galena (lead ore; PbS) has a smaller specific gravity
than halite (table salt; NaCl).
C. The specific gravity is a measure of how fast an object
will fall a distance of 1 m, in a vacuum.
D. The specific gravity of a particular mineral specimen
depends on the size of the specimen.
A
If a sample has good cleavage in three directions, and each cleavage direction is at right angles to the other two, then . . .
A. the crystal can be peeled apart into thin sheets.
B. the crystal grows to form cube-shaped crystals.
C. if struck with a hammer, a smooth fracture shaped like a clam shell forms.
D. when crystals break, little cube-shaped or brick-shaped fragments form.
B
Which of the following processes does NOT lead to the formation of a mineral or minerals?
A. Precipitation from an aqueous solution.
B. Instantaneous freezing of molten rock.
C. Slow cooling of molten rock.
D. Precipitation from concentrated gases.
E. Slow diffusion through a solid.
A
Silicate minerals dominate _______
crust and mantle.
True/False
In decreasing order of silicon content: • Felsic (or silicic) • Mafic • Ultramafic • Intermediate
False
- Felsic (or silicic)
- Intermediate
- Mafic
- Ultramafic
The SiO44- anionic unit: ________
the silicon-oxygen tetrahedron
What is the chemical structure of Silicate Minerals
- Four O atoms are bonded to a central Si atom.
- Define the corners of a four-sided geometric figure
- The silica tetrahedron is the building block of silicates.
Silicate minerals are divided into several classes based on _______
how the silica tetrahedra are arranged
How are gems cut and shaped for jewelry?
- Facets are ground onto a gem by a lapidary machine.
- Faceting a gemstone takes a lot of time and effort.
- Facets are not natural crystal faces.
