Minerals

[Most] rocks are [mostly] made of minerals, so ___________identification and interpretation depends on recognizing ____________________________________

Over _______ mineral types have been described, but only about ________ account for the bulk of most rocks. These are the “rock-forming” minerals.

Atoms: The Building BlocksNucleus: contains _____________ and _____________

Atomic Number: The number of ________in the __________

Atomic Mass: # of _____________ + # of ____________ in the nucleus.Electrons: “orbit” the nucleus, responsible for ______________ between atoms

+1

+2 +4+3 -1-2

Atoms will tend to form bonds such that their outer shells become full (or empty) by either donating or accepting electrons. Electrons carry a negative charge, so the overall charge of the atoms changes when electrons are transferred. The sizes of the atoms will change as well.

Bonds___________: transfer of electron(s) from donor ion (cation, +) to recipient ion (anion, -)

____________: sharing of _________(s)

___________: sharing of valence electrons across many atoms, resulting in a “cloud” of electrons permeating the crystal structure

Van der Waals: weak “tugging” of electron(s)

_________________ electrons tends to increase the _______________of the atom (ionic radius) whereas removing the tends to make it ________________. Note the difference between ferric iron (Fe3+) and ferrous iron (Fe2+). How will the size of an ion affect its ability to fit into a crystal structure?

Other Characteristics of Ionic Bonds• Common between elements in the 1st and 17th columns

(1A and 7A) or in the 2nd and 16th columns (2A and 6A).

Give examples:

• Strong under _____________________ but weak under _________(therefore promoting cleavage planes)..

• Produce highly symmetric crystals (such as cubic) of moderate ____________ and ___________.

• May dissolve ___________ in water, but typically have a _____________melting temperature.

• _______________conductors of heat and electricity.

Covalent BondsCovalent bonds arise from the sharing of electron(s) between adjacent atoms. The electrons may be shared equally, as above, or unequally, as with polar bonds. When hydrogen bonds with something other than itself, it usually forms a polar bond.

• _________ melting temperatures

• Produce crystals of lower symmetry but______________.

• Relatively _____________ in water.

• __________________ conductors of heat and electricity.

Metallic Bonds

Here, the electrons involved in the bonds are not associated with any particular atom but are ________to wander about the structure_.

These electrons can ______________ and ______________across a wide range of energies corresponding to visible light, producing the characteristic metallic luster of such materials (often metals).

Metals tend to be excellent _______________________ due to these “non-localized” electrons. They also typically ______________heat well.

Metals also tend to be _________________ (easily shaped by striking with a hammer), since the atoms can readily rearrange themselves in the midst of the swarm of surrounding electrons.

Van der Waals forces (also known as ___________ bonds) do not involve electron transfer, merely a “tugging” of the electrons of one atom towards a neighboring atom due to the polarization of the atoms themselves. For example, these polarizations may arise from unequal sharing of ___________ in covalent bonds.

Hydrogen bonds are quite ______, producing structures which easily __________ along the intervening planes (graphite shown here).

Van der Waals Forces

Five-Part Definition of a MineralTwo Questions:

1) Is it a mineral? First three parts.

2) Which mineral is it? Last two parts.

Question 1: Is it a mineral

1)_____________________. Useful for interpreting geologic phenomena.

2)_____________. Organic processes and materials will be considered separately.

3)___________. Strictly speaking, this means crystalline.

Question 2: Which mineral is it?

4) _______________________. A particular regular, periodic, ordered atomic arrangement.

5) _________________________, within a limited range. Allowable variation is determined case-by-case.

Are these minerals (circle yes ones):

Salt, sugar, cubic zirconia, glass, ice

Crystal faces may grow in differing proportions from sample to sample, but the angles between equivalent faces remain constant, controlled by structure at the atomic scale.

A cubic building block (unit cell) can produce several crystal shapes, but only those which are compatible with cubic symmetry.

Haüy (1781) proposed that crystals could be constructed from building blocks of identical shape and composition, stacked in a repeating pattern.

Within each crystal system (for example, cubic), many forms are possible. All such forms are consistent with the underlying _____________ of the system itself.

Useful Physical Properties

• _____________. Treacherous. Different minerals with same color, same mineral with different color.

• __________. Color of powdered mineral.

• _____________. How the surface reflects light.

• ____________. Scratch hardness, from 1 to 10 on the Moh’s hardness scale.

• ___________________. How the mineral breaks.

• Other. __________________________________________________________________________, etc.

COLOR: Color, is ________ a reliable property for mineral identification, generally speaking. It should be used only as a ____________, confirming characteristic. (Beryl = Be3Al2Si6O18)

_______________________ is tested by rubbing the mineral against an unglazed porcelain plate. The color of the powder is quite consistent from sample to sample.

Tips for streak testing:•The sample must be softer than the porcelain plate (about 6.5 on Mohs scale).

•Use a high-contrast background. White plate for dark streaks, black plate for light streaks.

•If the streak is white or colorless, use a different method of identification– most nonmetallic minerals fall into this category.

Luster

This refers to the manner in which the surface of the ______________, but is NOT just a question of how “shiny” it is.

First, consider whether the mineral resembles a piece of metal (metallic luster) or not (nonmetallic luster). ____________can be either bright or dull, however.

Luster describes the quality of reflection from the mineral’s surface. Above is galena (PbS) which has a bright metallic luster. It is NOT a piece of metal, it merely reflects light like a piece of metal. A surface which resembles dull metal is also said to have metallic luster.

NONMETALLIC LUSTERS

A few, arranged by decreasing ________________: adamantine, vitreous, resinous, pearly, waxy, silky, dull, earthy

Hardness• Mohs hardness scale is based on scratch

hardness, not indentation hardness.

• Scale was developed by Mohs (1812) using minerals as reference points.

• Mineral hardness can be ______________. It varies with the crystallographic direction in which it is measured.

• Report hardness as a range of possible values, depending on available tools.

Tall, Green Cumquats Fall All Over Queen Theresa’s Cute Dress

Cleavage Planes• Many (not all) minerals not only grow with flat

_______________, but also break along flat _____________ known as cleavage planes.

• Cleavage planes may or may not be in the same directions as crystal _____________________.

• Keep track of the _________ of planes (each plane has two sides), the __________ between them (90o or not 90°), and the ___________ of the cleavage.

• Cleavage will often appear as a series of __________ planes, while crystal faces will not.

Fracture• Fracture occurs in directions

along which ____________ are _____________.

• Some minerals will cleave and fracture, others only will fracture (such as quartz).

• Common types of fracture include _____________ (shell-like), _____________ (elongate fibers), and _____________ (like broken chalk).

Conchoidal Fracture

Splintery Fracture

Earthy Fracture

Other Useful Physical Properties

Many other mineral ID tests are possible, most of which are only useful in a few cases.

Examples include taste (not recommended in lab), reaction with dilute _________ (effervescence), ___________, radioactivity, fluorescence, and so forth.

Mineral Habit (Appearance/Growth Shape)

Mineral crystals seldom grow within an environment of unlimited resources, so they almost never achieve ideal geometric shapes.

Limitations of _____________, _________, and ___________will control the appearance in which the minerals are actually found. This appearance is known as the habit of the minerals.

A cubic mineral, such as garnet, may grow into any of these forms (among others) OR may display a shape that is a combination of faces from more than one form.

• Which crystal faces actually form.

• The relative sizes of these crystal faces.

• ______________.

• Aggregation of multiple crystals

Aspects of Habit

Some Typical Shapes• __________: needle-like

• ________: broad, flat, elongate

• ____________: branching, may resemble a “plant fossil” in the rock

• __________: plate-like

• __________: close to the same dimensions in all directions, also called equidimensional

Twinning may develop whenever there is more than one way to follow the “rules” of crystal growth, for example by switching to the mirror-image of the crystal structure. Twins may be _______________ (joined within a shared volume), ___________ (joined along a plane) or ______________ (multiply-twinned, often at a microscopic or submicroscopic scale).

Aggregations

Adjacent (but not necessarily twinned) crystals of the same mineral may develop distinctive patterns or arrangements.

The most common aggregation is ___________, which consists of small (often microscopic) interlocking grains. If the specimen “just looks like a chunk of rock” then it is probably massive. Massive does not mean______________.

Some Other Aggregations• Botryoidal: like a bunch of

grapes

• Columnar: parallel columns

• Druse: crystals projecting from a surface, often found in gift shops

• Radiating: outward from a central point

Crustal Crystal Chemistry

For every 100 atoms in Earth’s crust, there are approximately

____ O (oxygen)

____ Si (silicon)

____ Al (aluminum)

____ each Fe, Mg, Ca, Na, K

And a few Ti (titanium)

Everything else is ____________.

Some of the Mineral Groups• _____________________: composed of only one

element, which is unusual. Name is the element (except graphite and diamond). A few are: _________________

• _______: metal(s) plus oxygen, such as XO, X2O, X2O3, and XY2O4.Example:

• ____________: contain water as H2O or OH. For example:

• ___________: metal plus halide, usually F or Cl. For example:

More Mineral Groups• __________: metal(s) plus sulfur.

• ________: metal(s) plus sulfur AND oxygen.

• ____________: metal plus CO3.

• ________________: metal plus PO4.

• ______________: metal(s) plus silicon and oxygen.

Look on P 42 in your book for examples.

Silicates

• Oxygen and silicon account for over ____% of the atoms in the crust.

• About ____% of known minerals are silicates.

• About 40% of commonly occurring minerals are silicates.

• About ____% of the crust is made of silicates.

The silicate tetrahedron is the basic building block of the silicate minerals.

__________ ions are much larger than ______ ions, so the silicon fits in the space between four clustered oxygens.

By itself, this structure is __________________, since the four O2- have a net -8 charge and the Si has a +4 charge.

Charge balance is achieved by sharing oxygen atoms either with (a) other silicate tetrahedra or (b) other parts of the crystal structure.

Six Classes of Silicates1) Nesosilicates: isolated tetrahedra

2) Sorosilicates: paired tetrahedra

3) Cyclosilicates: rings of tetrahedra

4) Inosilicates: chains of tetrahedra, either single or double

5) Phyllosilicates: sheets of tetrahedra

6) Tectosilicates: 3-D framework of tetrahedra Name refers to carpentry (framework). Make up about _________% of the crust! Major groups: quartz and the feldspars

(see online notes for pictures of all classes of silicates)