Rocks

What is the difference between relative and absolute time?

Relative time gives a basic ideal of what came first, while absolute time tells you the exact age of an object.

Relative: sibling A is older than sibling B, but you don’t know their ages

Absolute: sibling a is 10 years old and sibling B is 8 years old.

How can the principles of superposition and cross cutting relationships be used to infer time?

Superposition: Uniform layers of rocks stack on top of each other. Oldest on the bottom and youngest on the top.

Cross Cutting: A uniform layer of rocks stacked on top of each other, but there is a section of rock cutting through the layers. The section that cuts through the rocks is the youngest section.

How old is the Earth?

About 4.54 billion years old

What is the difference between a rock and a mineral?

A mineral is a pure naturally occurring substance with a fixed chemical formula and crystalline structure, while a rock is a solid mixture made of one or more minerals.

What determines if a material is a mineral?

A mineral is a naturally occurring, inorganic, solid substance with a defined chemical composition, a crystal lattice structure, consistent physical properties, and geologic origin.

What is an ion?

An ion is an atom with excess positive or negative charge.

How do ions bond?

Ionic Bonding or Covalent Bonding

Ionic: One atom steals a proton from another atom. Example » a Chlorine atom steals a proton from Sodium atom. This gives the sodium atom a negative charge (anion) and the chlorine atom a positive charge (cation)

Covalent: Two atoms share one or more pairs of electrons to fill their outer shells.

What is a polymorph?

A mineral that shares the exact same chemical composition as another mineral, but has a different internal crystal structure.

Diamonds and Graphite are a great example of a polymorph. Diamonds form under extreme pressure, which makes a tight and rigid crystal lattice, while graphite form under lower pressure which makes it softer.

How do minerals form?

Crystallization from change in temp — magma solidifying

Crystallization from solutions in water — water evaporating

Crystallization caused by biological processes — shells

What are classes of minerals? Which are most common?

Silicates - Si4+, O2- combined with other cations (Most Common)
Carbonates - (CO3)2-
Oxides - (O)2- and metallic cations
Sulfates - (SO4)2- and metallic cations
Sulfides - (S)2- and metallic cations (Least Common)

What is the silicate tetrahedra? How are they bonded together to form different silicate minerals?

A silicate tetrahedron is a four-sided pyramid structure made of one central silicon atom covalently bonded to four oxygen atoms at the corners.

Silicate tetrahedra link together through a process called polymerization (sharing oxygen atoms) or connect via positively charged metal ions.

What are the 4 different kinds of silicate tetrahedra structural arrangements?

Single Tetrahedrons (Olivine and Garnet) » Tetrahedra do not share any oxygen atoms with each other. They are bound together independently by metal cations.

Single and Double Chains
Single: Pyroxene » Tetrahedrons share two oxygens with two other tetrahedrons to form a virtually endless chain. (Silicon-Oxygen ratio 1:3)
Double: Amphibole » Two single chains lie side by side so that all the right sided tetrahedrons of the left chain are linked by an oxygen to the left sided tetrahedrons of the right chain. (Silicon-Oxygen ratio 4:11)

Sheets (Muscovite, Biotite, Clay) » Chains of tetrahedra are linked by shared oxygens to other chains in a 2D plane that produced a sheet-like structure (Silicon-Oxygen ratio 2:5)

Framework (Feldspar, Quartz) » All four oxygen atoms are shared with neighboring tetrahedra, creating a tightly interlocked, robust 3D structure. (Silicon-Oxygen ratio 1:2) VERY COMMON

What is cleavage in minerals? Why does it occur?

Cleavage is a mineral’s tendency to break along smooth, flat, parallel planes.

Cleavage happens because some chemical bonds between atoms is weaker than others, so when pressure is applied the mineral splits along these microscopic lines.

Why do not all minerals have cleavage? If a mineral doesn’t have cleavage, how does it break?

Not all minerals have cleavage because some minerals have very strong bonds. Quartz is a good example because it has very strong bonds.

If a mineral does not break with cleavage, it fractures instead.

What is a special property that is useful to distinguish calcite?

Calcite reacts to acid.

What is the rock cycle? What processes convert igneous, metamorphic and sedimentary rocks into each other?

The rock cycle is a continuous natural process where Earth’s three main rock types transform from one type into another over geological time.

Rocks that are pushed deep into Earth melt into magma. That magma then cools either above or below the surface to make igneous rocks.

Rocks exposed to the surface will break down into sediment because of weathering and wind/water erosion. The sediment accumulates in layers, then compacts and cements to form a sedimentary rock.

When a rock is buried under the surface or squeezed by tectonic plates, extreme heat and pressure alter its mineral structure without melting it and turn it into a metamorphic rock.

What is the difference between intrusive and extrusive igneous rocks? Which is aphanitic? Phaneritic? Cooling history?

Intrusive (Plutonic) rocks form when magma cools slowly beneath the Earth’s surface.

Extrusive (Volcanic) rocks form when magma cools quickly on the Earth’s surface.

Aphanitic: Fine-grained texture where individual mineral crystals are too small to see without a microscope. (Extrusive)

Phaneritic: Coarse-grained texture where mineral crystals are large enough to see with the naked eye. (Intrusive)

Cooling History: Intrusive takes millions of years to form giving atoms time to make crystals. Extrusive cools quickly, which prevents large crystals from forming and makes a fine-grained or glassy texture.

What does a porphyritic texture mean and how was it formed?

A porphyritic texture is an igneous rock texture defined by large, well-formed crystals that are scattered inside a much finer-grained or glassy background called the groundmass.

Its formed when magma cools slowly underground to give time for the large crystals to form. Then, the magma is quickly moved to the surface (volcanic eruption), and the remaining liquid cools quickly, which freezes into tiny crystals or glass to form the groundmass. (Examples: porphyritic basalt or andesite)

What is the difference between mafic and felsic?

Mafic rocks have lower silica levels and a darker color.
Felsic rocks have higher silica levels and a lighter color.

What determines at what temperature a rock will melt? Do all rocks melt at the same temperature?

All rocks do not melt at the same temperature. Felsic rocks melt at lower temperatures because of its high silica levels, while mafic rocks melt at higher temperatures due to its low silica levels.

How do partial melting, magma differentiation and fractional crystallization relate to each other?

Partial melting changes rock into a special liquid and fractional crystallization refines the liquid as it cools. Together, they form the core of magma differentiation, which means that as the magma cools, it changes based on its surroundings.

If you have a uniform parent magma, will all the igneous rocks that cool from it be the same composition?

No, igneous rocks that cool from a uniform parent magma will not have the same composition.

What mineral forms at the highest temperature in a magma chamber? Which forms last? Why?

Olivine forms first at the highest temperature in a magma chamber. This is because Olivine has a simple, isolated silicate tetrahedron structure with high amounts of iron and magnesium. These bonds are simple so they form stably at a high heat.

Quartz forms last at the lowest temperature. This is because it has a more complex binding process, and only becomes stable at lower temperatures.

This is explained in Bowen’s reaction series

If you find an igneous rock in the field, how could you decide if it was formed in a sill or from a lava flow?

If a rock was formed in a sill (intrusive) then there would be a fine-grained texture and would lack weathering on the top and bottom.

if a rock was formed from a lava flow, then it would show more weathering and may have a bubbly surface from gas bubbles.

What is viscosity? How does viscosity vary with composition of magma?

Viscosity is a fluid’s resistance to flow. Magma that is high in silica (Felsic) will be thicker and sticky, which means that it would have a high viscosity.

Magma that is low in silica (Mafic) will be flow easily and quickly, which means that it has a low viscosity.

How do metamorphic rocks form?

Metamorphic rocks form when existing rocks are transformed deep underground by intense heat, immense pressure, and hot chemical fluids without actually melting.

What is the difference between recrystallization and neocrystallization? Are these changes based on temperature or pressure?

Recrystallization changes the size and shape of mineral grains.

Neocyrstallization forms entirely new minerals with different chemical compositions.

Both processes are driven by a combination of temperature and pressure

How does changing pressures and stresses influence texture of metamorphic rocks?

Changing pressures and stresses changes the texture of metamorphic rocks by physically rearranging, rotating, or resizing mineral crystals.

What is a porphyroblast?

A large mineral crystal that grows within a finer-grained matrix of a metamorphic rock. (Example: Garnet)

How does contact metamorphism differ from regional metamorphism?

Contact metamorphism changes rocks using high heat from nearby magma.

Reginal metamorphism changes rocks using both heat and intense pressure over a large area.

How are clastic (detrital) sedimentary rocks formed from other rocks?

Clastic rocks are formed through weathering, erosion, deposition, compaction, and cementation.

What is the difference between erosion and weathering?

Weathering is the breaking down of rocks into smaller pieces without moving them.

Erosion is when rocks are worn away and transported to new locations by water, ice, wind, and gravity.

How does grain size, rounding and sorting of sediments change as they are transported away from their source?

As sediments are transported away from their source, the grain size decreases, rounding increases, and sorting improves.

What is the difference between breccia and conglomerate?

Breccia » Made up of angular clasts, not weathered much before becoming rock, deposited close to their source

Conglomerate » Made up of rounded clasts, weathered a lot before becoming rock, traveled far from their source.

What type of environment is shale formed in?

Shale forms in low-energy, quiet-water environments.

What type of environment is sandstone formed in?

Sandstone forms in moderate to high energy environments with moving sand

What type of environment is arkose formed in?

Arid or cold terrestrial areas close to the source rock.

What type of environment is conglomerate formed in?

high-energy environment with moving water and rounded pebbles.

What type of environment is breccia formed in?

High-energy areas very close to the source of the rock fragments.

(key for these types of questions: lower energy = finer grains, higher energy = larger grains)

What is the difference between a high energy and low energy sedimentary environment?

High energy: water/wind motion is fast, the sediment is larger, and rocks that form are breccia or conglomerates.

Low energy: water/wind motion is calmer, sediment is very fine grained, rocks that form are shale, siltstone, or fine limestones.

What type of environment are carbonate/biochemical sedimentary rocks formed in?

Sedimentary rocks that come from living organisms

Formed in warm, shallow, clear water with lots of oxygen and agitated by waves.

What type of environment are organic sedimentary rocks formed in?

Made from organic carbon.

The carbon accumulates in water saturated environments that lack oxygen.

What type of environment are chemical/evaporate sedimentary rocks formed in?

They are formed in arid saline environments where the rate of water evaporation greatly exceeds the rate of water input.

How can structures in sedimentary rocks give information about depositional environment?

Sedimentary structures give clues about ancient environments by recording the physical processes, energy levels, and transport directions active when sediments were laid down.

What are properties of minerals that are useful for everyday use?

Hardness, luster, durability, conductivity, density, chemical stability, and low solubility. Examples: quartz in glass, gypsum in drywall, coper in wiring.

What is an ore?

A rock or mineral deposit that contains a valuable material in high enough concentration to be mined at a profit.

What is an acid mine drainage area?

A site where water reacts with exposed sulfide minerals from mining, producing sulfuric acid and dissolved metals. The result is acidic, orange/red-stained streams that harm aquatic life.

What are environmental impacts of mining?

Habitat destruction, soil erosion, acid mine drainage, water contamination, air pollution and dust, land subsidence, and large, waste volumes.

What is mined in NY state?

Some materials mined in NY are: salt, sand/gravel, crushed stone (limestone), garnet, talc, and gypsum.

What is the relationship between mining and weathering and erosion?

Mining exposes fresh rock to weathering, speeding up chemical breakdown, and physical breakdown. Removing vegetation and soil increases erosion and sediment transport.

What are some uses of sand?

Sand can be used for glass making, concrete and construction, filtration, fracking, and beach replenishment.

What ore material is associated with hydrothermal environments?

Some ores that are associated with hydrothermal environments are galena, sphalerite, chalcopyrite, gold, silver, and quartz veins.

What ore material is associated with igneous environments?

Some ores that are associated with igneous environments are chromite, magnetite, platinum, nickel, and diamonds.

How does coal form?

Plant material accumulates in swampy, low-oxygen conditions, and form peat. Burial, heat, and pressure over millions of years drive off water and volatiles, increasing carbon content.

How does coal rank change C content, energy and CO2 emissions?

Higher rank (anthracite) means higher carbon content and higher energy per unit mass. CO2 emitted per unit of energy is generally similar to slightly higher for higher ranks, while lower ranks (lignite) produce more CO2 per unit energy because of higher moisture and lower energy content.

How do oil and gas form?

Marine organic matter is buried in fine sediment and heated with depth. Kerogen forms, then oil at about 60 - 120 Celsius and gas at higher temperatures.

What is the difference between a source rock and reservoir rock?

A source rock is a organic-rich (shale) and generates hydrocarbons. Reservoir rock is porous and permeable (sandstone, limestone) and stores and allows flow of hydrocarbons.

Why is fracking used to extract shale gas and shale oil?

Fracking is used because shale is a source rock with very low permeability, so hydrocarbons cannot flow to a well naturally. Fracking creates fractures that open pathways.

What is fracking?

Fracking is injecting high-pressure water, sand (proppant), and chemicals into a well to fracture rock and release trapped oil and gas. The sand keeps fractures open.

What are critical minerals? What determines if a mineral is critical?

Minerals essential to the economy or national security that have supply risk.

A mineral is determined to be critical if it is economically important, is only available in very few countries, and there are not many substitutes.

What is a difference between mineral resource, reserve, production and ore?

Resource: total known or estimated amount of a mineral, including material not yet economical to extract

Reserve: The portion of the resource that is economically and legally executable now.

Production: The amount actually mined in a given period.

Ore: The rock itself that contains the valuable mineral in minable concentration.