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• A mineral relates to a rock in the same way that an atom relates to a molecule

Rocks and Minerals

• A rock is a solid combination of mineral grains, older rock fragments, or natural glass
• Minerals are the building blocks of our planet that make up most rocks and sediment
• There are over 4000 identified minerals
• Minerals are useful resources that can be dangerous and fascinating

Definition of a Mineral

• In food science, minerals aid the body's normal functionality
• A basic definition of a mineral is that it is neither plant nor animal

Geological Definition of a Mineral

• Minerals are homogenous, naturally occurring, solid, inorganic substances
• They have a definable chemical composition and an internal structure arranged in a lattice made of orderly atoms, ions, or molecules

Naturally Occurring Minerals

• A true mineral forms naturally through Earth processes
• Synthetic minerals are lab-grown and man-made materials like steel and plastic are not minerals

Earth Processes

• Solidification forming from melts is an earth process that creates minerals
• Precipitation, usually due to evaporation, an earth process
• "Biogenic minerals" are formed by organisms
• These minerals are chemically identical to naturally occurring non-organic minerals like calcite and apatite

Minerals as Solids

• A mineral is a material that maintains its shape indefinitely
• Minerals cannot be liquids

Organic vs. Inorganic Minerals

• Minerals must be inorganic
• Organic molecules include carbon-carbon or carbon-hydrogen bonds
• Sugar (C12H22O11) is an example of an organic molecule

Chemical Composition of Minerals

• A mineral must have a definable chemical formula
• Some minerals contain only one element, like graphite or diamond (C)
• Most minerals are compounds of two or more elements, like quartz (SiO2)

Crystalline Structure

• Minerals must have a crystalline structure
• The atoms in a mineral must occupy fixed positions in a grid called a lattice
• Solids lacking atomic order are called glasses
• Most solid materials are crystalline

Crystals

• A crystal is a single, continuous piece of crystalline solid bounded by flat crystal faces
• Crystal faces grow naturally as the mineral forms reflecting the atomic structure
• Equivalent faces on different samples of the same mineral will have the same angular relationship

Atomic Bonding

• The geometry of atomic packing and the nature of chemical bonding determine the mineral properties
• How elements pack into a mineral crystal lattice depends on the size and charge of the element's ions
• Anions are usually larger than cations
• A large central cation needs a larger number of anions, while a smaller cation needs fewer anions

Mineral Polymorphs

• Diamond and graphite are polymorphs of carbon
• The diamond lattice has a tetrahedral arrangement, where graphite has a sheet arrangement
• These minerals share a chemical formula but have different properties
• The different properties result from the different types of atomic bonds

Crystal Growth

• Growth occurs as atoms attach to the outer surface
• Crystal faces grow perfectly in an open cavity
• Early crystals serve as seeds for the mineral's further growth

Types of Crystals

• Crystals often encounter other growing crystals while growing
• Three types of crystals are euhedral, anhedral, and subhedral

Mineral Identification

• Minerals are identified based on physical and chemical properties
• These properties depend on chemical composition and crystal structure
• Mineral identification is a skill requiring learning mineral properties and test methods

Mineral Characteristics

• Minerals are identified based on the following characteristics:
• Color
• Streak
• Luster
• Hardness
• Specific gravity
• Crystal habit
• Cleavage (or fracture)
• Reaction to acid
• Special properties

Color

• Color is the part of the visible light spectrum that is not absorbed by the mineral
• Color is a solid diagnostic for some minerals, like malachite, but a poor indicator for others like quartz
• Avoid using one mineral to describe another

Hardness

• Hardness is the scratching resistance of a mineral
• Hard minerals can scratch soft minerals
• Directly linked to atomic bond strength
• The Mohs hardness scale helps determine a mineral's hardness

Streak

• Streak is the color of a crushed mineral powder left on an unglazed porcelain plate
• Minerals may have a different streak color than their outward color

Luster

• Luster is a property describing how a mineral surface scatters light
• The two main luster subdivisions are metallic and nonmetallic

Specific Gravity

• Specific gravity is a mineral's density defined as the ratio of its weight to the weight of an equal water volume at 4°C
• Proficiency with specific gravity can develop by hefting minerals
• A piece of lead "feels" heavier than a similar-sized quartz

Crystal Habit

• Crystal habit refers to the shape of a single crystal with well-formed faces or aggregates of many well-formed crystals
• Crystal habit is described with common geometric shapes, such as:
  • Cubic
  • Prismatic
  • Bladed
  • Platy
  • Needle-like
  • Fibrous

Special Properties of Minerals

• Effervescence (reactivity with acid) - calcium carbonate
• Magnetism - magnetite, pyrite, hematite
• Taste - halite
• Smell - sulfur
• Feel (tactile response) - talc
• Striations - plagioclase
• Marking on paper - graphite

Cleavage

• Cleavage is the tendency for a mineral to break along lattice planes with weaker atomic bonds
• Mineral cleavage forms distinct planar surfaces with defined orientations
• These surfaces are referred to as cleavage planes

Distinguishing Cleavage Planes

• Cleavage planes may be hard to distinguish from crystal faces

Fracture of Minerals

• Minerals lacking lattice planes of weakness and with equally strong bonds in all directions fracture instead of cleaving
• Conchoidal fractures exhibit smooth, curved surfaces