EASC 1000 - Topic 2

Element

The most basic component of chemistry. A substance that cannot be resolved into simpler substances by chemical means. There are 92 naturally occurring and they appear on the Periodic Table.

Atom

The smallest particle of an element that still retained all the physical and chemical properties of said element. The most basic unit of an element. Made up of three atomic particles:

• Protons (1+) - in the nucleus, dictates an element’s atomic number

• Electrons (1-) - orbit around the nucleus

• Neutrons (0) - in the nucleus

Electrical neutral due to protons and electrons canceling each other out.

Ions

Electrically charged atoms. Made by atoms who achieve a full 8 electrons in their outermost electron shell through gaining, losing, and sharing electrons with other atoms.

Cations

Positively charged ions which have lost electrons in order to achieve the 8.

Anions

Negatively charged ions which have gained electrons to achieve the 8.

Compounds

When two or more elements combine chemically (minerals are a sub-group of these).

Molecule

The smallest unit into which a compound can be broken down and still retain all the physical and chemical properties of that compound.

Chemical Bonds

Hold atoms together in molecules and are electric in nature — positive attracting negative. Results in a change of the electron shell configuration of the atoms involved, but no change in the nucleus of these atoms. There are 4 basic types: Ionic, Covalent, Metallic, and Van der Waals.

Ionic bonds

Form when one atom transfers an electron to another atom.

Covalent bonds

Form when one atom shares an electron with another atom.

Isotopes

When something is the same element (same number of protons and electrons), but has a different atomic mass (number of neutrons). Have the same chemical properties, but different physical properties, and are the reason why atomic masses of elements cannot be whole numbers. (Ex: carbon has 3 isotopes, its atomic mass is 12.011).

Atomic Radius

The distance between an atom’s nucleus and the outermost electron shell/orbit.

• Increases from left to right on PT.

• Increases down a group as you add motor energy levels to the atom.

Electronegativity

An atom’s tendency to attract electrons involved in bonding.

• Increases from left to right on PT

• Decreases from top to bottom along a group on PT

Exceptions are noble gasses, lanthanide, and antinides.

ionization Potential

Energy needed to remove an electron from the outermost shell of an atom in its neutral state.

• Increases from left to right on PT

• Decreases from top to bottom on PT

Mineral

• Naturally occurring - Formed by geological processes NOT synthetically by us

• Solid - Must retain its solid state. Even though oil and gas are naturally occurring, they’re not solid and therefore not considered minerals.

• Inorganic - Cannot be made of C-C or C-H-O bonds which are found in living organisms or are like those of living organisms.

• Specific chemical composition - Must have a defined chemical formula.

• Crystalline form/structure - Where the atoms are fixed in an orderly pattern by chemical bonds, has a 3-D structure arrangement of atoms or ions with a specific geometry.

Solidification

The process of forming minerals through the freezing of a liquid. Ice crystals grow from water, crystal grow from cooling magma, etc.

Precipitation

The forming of minerals through growth from a fluid rich in atoms/ions (supersaturated liquid). Salt crystals from seawater.

Solid-State Diffusion

The movement and rearrangement of atoms or ions through a solid into a new crystal structure. Metamorphic mineral growth under high temperatures and pressure.

Biomineralization

When organisms extract ions from water and facilitate mineral precipitation. Shells of clams.

What’s another way to form minerals?

Through precipitation from a gas.

Anhedral crystals

When a mineral’s growth becomes restricted in one or more directions, and their shapes do not have crystal faces but are instead controlled by their surroundings.

Crystal

Single, continuous piece of crystalline material bounded by flat surfaces (crystal faces) that form naturally as a it grows.

Colour

Minerals absorb certain wavelengths from whole spectrum visible light. The visible colour represents the wavelengths not absorbed by the mineral. Not often a diagnostic property.

Streak colour

The colour observed when a mineral is pulverized into a powder. Often tested using a “streak plate” made of porcelain — this only works if the mineral is softer than the porcelain.

Lustre

The nature in which light is reflected or scattered from a mineral surface. Defined based on metallic vs non-metallic. Non-metallic lustres have more more descriptions:

• Vitreous

• Resinous

• Pearly

• Earthy

Hardness

A mineral’s ability to resist scratching. Reflection of the ability pf bonds in the crystal structure to resist breaking. Stronger bonds = harder, and covalent bonds are typically stronger than ionic. Measure using the relative scale of “Mohs Hardness.”

Relative scale of “Mohs Hardness”

A mineral can scratch a softer mineral only, not vice versa.

• Fingernail - 2.5

• Copper penny - 3.5

• Glass/steel - 5.5

• Steel file - 6.5

Specific Gravity

The density of a mineral measured relative to that of an equal volume of water at 4 degrees Celsius (the weight).

Crystal Habit

The shape of a crystal when it grows unimpeded with well-formed crystal faces (ephedral crystals), or as an aggregate of many crystals together. Reflection of the internal arrangement of atoms. Described using:

• Equant

• Cubic

• Prismatic

• Tabular

• Bladed

• Fibrous

• Needle-like

Special Properties

A mineral can be “effervescent” meaning they react with acid to produce gas. Or, “magnetic” such that it attracts metal. Or, some minerals give off a “fluorescent” glow when exposed to some wavelengths of electromagnetic radiation.

Fracture and Cleavage

Minerals break apart in different ways depending on the atomic arrangement in their crystal structures. Cleavage breaks along distinct planar surfaces of weakness that are parallel to a specific orientation of the crystal structure. Fracture is when there is no preferred planes that they break along. Reflects their atomic structures being equally strong in all directions.

How do you distinguish between cleavage and crystal faces?

Crystal faces are flat, continuous faces that are distinguished by being the only external feature of euhedral crystals.

Major classes

Silicates, sulfides, oxides, halides, carbonates, native metals, sulfates, and phosphates.

Silicates

A major class of minerals. SiO4 is their structural foundation. Dominates all of the composition of Earth’s crust and mantle.

Sulfides

A major class of minerals. Have a metal cation bonded to a sulfide anion. Much rarer than silicates. Generally dense (high specific gravity) and have a metallic lustre.

Oxides

A major class of minerals. Have a metal cation bonded to an oxygen anion. Can form in different environments from the mantle all the way to the surface. On the surface they’re often formed from reactions of other minerals with our oxygen-bearing atmosphere, giving the “rusty colour” we see in soil or on exposed steel.

Ionization Potential

The energy needed to remove an electron from the outermost shell of an atom in its neutral state.

Crystal Structures

Excellent examples of patterns formed in nature, in this case dictated by the spacing of atoms and chemical composition of the mineral. The patterns of crystals produce symmetry, whereby one part of the structure is a mirror image of an adjacent part. Often represented using a cluster of balls packed together in a fixed order which represent atoms/ions/ionic molecules, and sometimes sticks are used to illustrate bonds between them.

Physical Mineral Properties

Identifiable properties of a mineral that you can just see either with your eyes, or be found through handling and interacting with the specimen.

Halides

A major class of minerals. Have a halogen or “salt-producing” ion as their anion. Can form in different environments on Earth, from iron-rich seawater where the salt minerals can precipitate, to inside the crust where minerals can precipitate from hydrothermal fluids.

Carbonates

A major class of minerals. Have the CO2 molecule as their anionic group. Generally form near the surface of the Earth by precipitation from water, with or without the aid of organisms. Usually light coloured, soft, and effervescent.

Native Metals

A major class of minerals. Are comprised entirely of a pure mass of a single metal element where the atoms of the metal are bonded with metallic bonds. Some examples are gold, silver, and copper. They’re prized and areas where they’re concentrated are only targets to economic geologists.

Sulfates

A major class of minerals. Cations are bonded to SO4 anionic groups. Most are formed near the surface of the Earth, precipitated from evaporating salty seawater or in caves. Some can also precipitate from “black smoker” fluids on the ocean floor.

Phosphates

A major class of minerals. Cations are bonded to PO4 anionic groups. Can crystallize from magmas or precipitate from hydrothermal fluids or by living organisms, where many bones, teeth, or scales are made of phosphate minerals.

Silica Tetrehedron

The building block of the silicates mineral class, where different configurations of them are sub-divided based on how much linkage there is between them, the geometry of the linkage, and the distribution of other cations between them.

• A pyramidal shaped structure that is comprised of 4 O atoms surrounding one Si atom.

How does the joining (polymerization) of silica tetrehedra work?

They join by sharing one or more of the 4 O atoms in their structure. Different groups of silicates are defined by changing amounts of O sharing between adjacent tetrahedra. As they join, different geometric patterns develop, and the ration of Si to O atoms in the mineral structure changes.

• Chains

• Rings

• Sheets

• And, more complicated 3-D networks.

Independent Tetrahedra silicates

Simplest case for silica tetrahedra where they remain isolated from one another in the mineral crystal structure (do not share any O atoms). Ratio of Si:O here is 1:4.

• Example: Olivine.

Single Chain Silicates

Chains of silica tetrahedra polymerize by sharing 2 O atoms each. The single O chain leaves 2 O free and generates the effective formula of SiO3. Joined by cations between them to achieve charge neutrality in the silicates.The ration of Si:O here is 1:3.

• Example: Pyroxene group

Double Chain Silicates

Have two chains joined by sharing an O atom every second tetrahedra. The joint of two single chains through a shared O leaves some tetrahedra with 2 unpaired O and others with 1 unpaired O, leaving an effective formula of Si4O11. Joined by cations between them but can accommodate a wider range of cation sizes. The ration of Si:O is 4:11.

• Example: Amphibole Group.

Sheet Silicates

Form by joining 2 double chains together through the sharing of another O atom such that all 3 corners of the base of a tetrahedra are shared. Leaves 1 unpaired O per tetrahedron and an effective formula of Si2O5. The bonding creates 2-D sheets with strong bonds and sheets are joined together in layers with cations between to reach charge neutrality. The ratio of Si:O is 2:5.

• Example: Clay minerals and micas.

• Creates a a diagnostic cleavage pattern (basal cleavage; 1 direction).

Framework Silicates

Have all O atoms of a tetrahedron shared with neighbouring tetrahedra. Leaves two O anions for each Si cation which achieves electrical neutrality without requiring any additional cations. Form 3-D network structures.

• Example: Quartz, Feldspars

Ring Silicates

Have silica tetrahedra joined together in rings by each tetrahedron sharing 2 O atoms. 6-membered rings are most common. the rings stack together to produce “tubes” often resulting in prismatic minerals. All rings have a Si:O ratio of 1:3.

• Example: Tourmaline and beryl.

Mineral Evolution / Mineralogy in the 4th dimension / Historic mineralogy

Examines the changes in the amount and diversification of mineral types through time with links to changes in different geological processes, the atmosphere, and biosphere of Earth. Minerals that can form depend on the chemical ingredients available and the conditions around them (pressure, temperature, etc). But, most of these minerals required fundamental changes in the evolution of life before they could form.

• Dr. Robert Hazen sub-divided Earth’s mineral evolution into 3 Eras and 10 Stages.

Prenebular minerals (before planets)

After the big bang, the only elements were H and He with a small sprinkle of Li. It took the early stages of star formation to form slightly heavier elements, and finally exploding stars to produce small amounts of heavier elements on the periodic table.

Era 1 - Planetary accretion

• Stage 1 - The first condensation of minerals in our early solar system from gasses and dust.

• Stage 2 - The first solid/mineral accreted to miniature planets that were able to melt and form a metal core surrounding by silicate minerals and also undergo metamorphic reactions and even fluid alteration.

Era 2 - Crust and Mantle Reworking

Processes that further separate elements into different reservoirs (lithosphere, atmosphere, hydrosphere). Changes the range of pressure, temperature, and availability of different gases in areas of mineral formation. And the unique role of life (biosphere) in being able to use elements to gain energy and in doing so make the first “bio minerals.”

• Stage 3 - Early igneous processes and other processes such as melting, crystallization of different minerals from a melt, etc.

• Stage 4 - Planets with enough internal heat can partially remelt the first rocks formed from melting and crystallization and make granites and pegmatites.

• Stage 5 - The oceanic and continental crust of Earth is constantly in motion due to Plate Techtonics.

Era 3 - Biologically Mediated Mineralogy

Abundant and diverse forms of life to make Earth unique in the Solar System, and life transforms the surface parts of Earth.

• Stage 6 - Mostly bacterial life that helped with precipitating bio minerals that could already form abiologically.

• Stage 7 - Great oxidation event where things changed in a geological instant when Cyanobacteria evolved the ability to make O2 as a byproduct and it accumulated in the atmosphere. More than 2500 minerals added

• Stage 8 - Boring billion

• Stage 9 - Snowball Earth events, reign of ice as the dominant mineral on the surface during these events, some associated with precipitation of carbonate sedimentary rocks.

• Stage 10 - Phanerozic era of biomineralization, new bio minerals able to be formed by complex life (ex: skeletons, shells). Evolution of land plants, increase rates of weathering, expansion of oxides and clay minerals at surface.