34 terms

Geol 101: Minerals

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Crystal
a single continuous piece of crystalline solid, typically bounded by flat crystal faces
-faces grow naturally as the mineral forms and reflect atomic structure
-structure is defined by the Geometry of Bonds between Atoms
Gemstones
single-crystal minerals that are
-Durable
-Rare
-Beautiful, as described by the 5 C's
• Clarity
• Color
• Carat
• Cut
• Certification
Minerals
1. naturally occurring, formed by geologic processes
2. inorganic crystalline solids
3. a definite chemical composition
mineral families
native elements, sulfides, halides, oxides and hydroxides, carbonates and nitrates, borates, sulfates, phosphates, and organic compounds
Silicates
most important family of rock-forming minerals Silicon and oxygen
-the most abundant minerals on Earth
-are divided into several classes based on how the silica tetrahedra are arranged
Silica Tetrahedron
This is the fundamental building block of all silicate minerals.
The Law of Constancy of Interfacial Angles
says that equivalent faces found on two samples of the same mineral always bear the same angular relationship
Oxides
Oxygen bonds with metallic cations to form important ore mineral oxides.
Sulfides
Sulfide (S-) combines with metallic cations to form many of our most important metal ore minerals.
Sulfates
contain the SO42- anionic group
-Many form via evaporation of seawater. Examples: gypsum (CaSO4 - 2H2O), anhydrite (CaSO4)
Halides
minerals that have halogens (F-, Cl-, I-, Br-) as their dominant anion
- Common ones include fluorite (CaF2) and halite (rock salt—NaCl).
Carbonates
contain the carbonate anion (CO32-)
-are soft minerals that fizz in dilute hydrochloric acid (Hal)
-Calcite and dolomite are common
Native Elemental
Native metals are minerals that occur as a single element.
Rock Cycle
Igneous rock can change into sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock. Igneous rock forms when magma cools and makes crystals.
Igneous Rock
-Molten Rock
*Usually with dissolved gasses
-Generated by melting mantle rocks
-"Lava" if magma reaches surface
-"Pluton" if magma stuck at depth
-Controlling Factors:
*Temperature
*Pressure
*Mixing or Assimilation of Host Rocks
Metamorphic Rock
-Core of Mountains
-Changes to original rock texture or mineral assemblage by temperature or pressure
-Controlling Factors on Metamorphic Rocks:
*Composition of Parent Rock
*Temperature
*Pressure
Sedimentary Rock
-Clastic
*Pieces of other rocks (e.g. sandstone)
-Chemical
*Precipitated from dissolved solution (e.g. salt)
-Organic
*Remains of organisms (e.g. coal or fossils)
Mineral Resources
-Metallic
*Gold
*Silver
*Copper
*Lead
*Zinc
*Iron
*Aluminum
-Nonmetallic
*sand and gravel
*Gypsum
*Halite (salt)
*Phosphate
*Dimension stone
What is a metal?
Opaque, shiny, smooth, solids that conduct electricity. These properties derive from metallic chemical bonds with delocalized electrons that move from atom to atom easily.
ductile
able to be drawn into thin wires
malleable
able to be hammered into thin sheets
Foliated Rock
Refers to repetitive layering in metamorphic rocks. Each layer may be as thin as a sheet of paper, or over a meter in thickness.
What is an ore?
Rock with metal-rich minerals that are concentrated enough to be economic to mine. This requires that metals are able to be extracted from the minerals without excessive expense.
How do ore deposits form?
geologic processes:
Magmatic activity
Hydrothermal alteration
Secondary enrichment
Groundwater transport (MVT)
Sedimentary processes
Residual weathering
Hydraulic sorting
Magmatic deposits
form from a cooling plutonic intrusion
Hydrothermal deposits
are formed by the action of hot water, which is very chemically reactive
-are also associated with black smokers at mid-ocean ridges
Secondary-enrichment deposits
Form when groundwater leaches and oxidizes primary sulfide ores. The water adds O2, OH, and CO2, forming a new suite of minerals.
Groundwater transport
creates Mississippi Valley-type (MVT) ores
hydraulic sorting
In high velocity water results in the formation of placer deposits. Low-density minerals are suspended and washed away while high-density grains are concentrated by settling out.
ore exploration and production
Mineral exploration involves systematic geologic investigation using advanced technology.
Geophysical surveys—magnetism, gravity, radioactivity
Geochemical surveys—water, sediment, soil, and biota Sometimes advanced technology is not needed. For instance, enrichment may be indicated by brightly colored rock and soil. Once identified, the dimensions of a potential ore deposit are determined by geophysical response augmented by core drilling and geochemical assay. A shallow ore body is removed by open-pit mining. A deeper ore body necessitates underground mining.
nonmetallic mineral resources
Society uses many geologic materials that don't contain metals. These materials are called industrial minerals and include dimension stone, crushed stone, concrete, gypsum, phosphate, sand, salt, and other geologic materials.
Dimension stone
Consists of rock slabs that are used as building materials. The rock is selected for visual appeal and durability. Cut and polished rock slabs are highly prized.
How long will mineral resources last?
Mineral resources formed as the result of geologic processes, which are too slow to generate new deposits. Thus, once mined, mineral resources are gone
environmental impacts of mining
-Mineral extraction and processing leaves a big footprint. Open-pit mines are large scars on the landscape.
-Mining creates huge volumes of waste tailings. Tailing piles are often acidic and laden with toxic metals. Unvegetated tailing may be sources of dust and runoff.
-Sulfides react with water and O2 to form sulfuric acid (H2SO4). This is known as acid mine drainage (AMD).
-Water from sulfidic spoil piles is acidified (pH <5.7) by sulfuric acid. The acidity dissolves iron, which then coats streams in rust. AMD mobilizes heavy metals and kills stream biota.