The Book of Earth

As a geologist looks and thinks about the earth, he can see that geologic time is much like chapters in a book while rocks play sentences, minerals play words, and atoms play the letters. The book covers the world from its origin to where we are today, detailing only that from the lithosphere, but also from the biosphere, hydrosphere, and atmosphere; we will, for now, focus on the lithosphere. I will only briefly speak about atoms because the further you go the more I digress from minerals.

Letters Of the Earth

All things are made of atoms: they are tiny particles that constantly move around, attracting and repelling one another. The word "atom" is derived from the greek 'atomos'  meaning indivisible. We know, now, that atoms are divisible. The atom is composed primarily of protons, neutrons, and electrons; protons are positive, neutrons are neutral, and electrons are negative, yet even then the atom just like the rest of the world is composed of mainly space. If you are familiar with Chemistry then you know about the periodic table of the elements. "Elements are presented in increasing atomic number; while rectangular in general outline, gaps are included in the rows or periods to keep elements with similar properties together, such as the halogens and the noble gases, in columns or groups, forming distinct rectangular areas or blocks (Gray)". The columns represent the groups and the rows represent the periods that the elements are classified under.

Words of the Earth

Most minerals are compounds, which means that they are combinations of elements. Some minerals are elements by themselves. Chemical bonding is the process by which atoms append to form compounds yielding minerals; you see these compounds bonded together by different bonds like ionic, covalent, van der vaals, and metallic, yet we mainly see ionic and covalent bonds.

In the earth's crust you see that about 98% of  it is composed of 8 elements. They are 46.6% Oxygen (O), 27.7% Silicon (Si), 8.1% Aluminum (Al), 5.0% Iron (Fe), 3.6% Calcium (Ca), 2.8% Sodium (Na), 2.6% Potassium (K), and 2.1% Magnesium (Mg).These elements are the matter in which these minerals are composed.

What is a mineral? 

A mineral is anaturally-occurring,homogeneous solidwith a definite, butgenerally not fixed,chemical composition and an orderedatomic arrangement.It is usually formed byinorganic processes.

1. A naturally occuring synthetic compounds are not known to occur in nature and cannot have a mineral name. However, it may occur anywhere, other planets, deep in the earth, as long as there exists a natural sample to describe.

2. A homogeneous solid meaning a mineral must be chemically and physically homogeneous down to the basic repeating unit of the atoms. It will then have absolutely predictable physical properties (density, compressibility, index of refraction, etc.). This means that rocks such as granite or basalt are not minerals because they contain more than one compound.

3. Definite composition of atoms or groups of atoms must occur in specific ratios. For ionic crystals (i.e. most
minerals) ratios of cations to anions will be constrained by charge balance, however, atoms of similar charge and ionic radius may substitute freely for one another; hence definite, but not fixed.

4. Orderly atomic structure is that crystalline materials are three dimensional periodic arrays of precise geometric arrangement of atoms. Glasses such as obsidian, which are quasi-solids, liquids (e.g., water, mercury), and gases (e.g., air) are not minerals.

5. Inorganic processes mean that it was not made by life, so crystalline organic compounds formed by
organisms are generally not considered minerals. However, carbonate shells are minerals because they are identical to compounds formed by purely inorganic processes.

10 General Properties for Minerals

CLEAVAGE 

It is the tendency of crystalline materials to split along definite crystallographic structural planes; typically you will look at the number of cleavage directions and the shapes that it breaks into. This is one of the most used properties to identify a mineral. Cleavage describes the way a mineral breaks along its plane of weakness; the plane of weakness is based on the atomic bonding in the exact point where the bonding is at its weakest, so this happens whenever the mineral is placed under stress in whatever form this may be.

FRACTURE

Fracture is what I would say is also one of the most defining characteristics of identifying a mineral. It described the shape and the texture along the surface of the mineral where the fracture has taken place. All minerals exhibit fracture, but sometimes it can be disguised if the cleavage is most obvious. Conchoidal, Earthy, Hackly, Splintery, and Uneven are the main types of fractures.

The most common I can think of would example of conchoidal fracture in a mineral would be flint. Obsidian is the go to guy for that type of fracture, but it is not actually a mineral.

Hackly fracture is most common in native elements that are represented also as minerals. The term hackly refers to the fracture appearing torn. Below is an example in the native element mineral Gold.

Earthy fracture is also a common type of fracture that you may see, and it is most easily identifiable by the fact that it appears as though it just came out of fresh sediment. One of the best examples of earthy fracture is the mineral limonite with a picture available below.

Splintery fracture is one that is noticeable by elongation in the mineral. The one I think of first is chrysotile; it may sound familiar because it is the most common source of asbestos. It is easy to see in a mineral such as chrysotile due to its fibrous appearance.

Uneven fracture is also really common; when I work on the oil rig, pyrite is a very common mineral to see. 

COLOR

Color can be useful in identification of minerals, but not as much as one may assume. It should only be an indicator for certain minerals; the deceiving thing about minerals is that they may be a different color, yet still be the same mineral. One good reference for this would be quartz due to its occurring state, it may be pink, colorless, purple, red, and etc.
 

CRYSTAL FORM

Crystal form can play a vital role in mineral identification due to minerals usually taking the same forms. Of course, nature never likes to be pigeonholed, so we know that some minerals may occur in different crystal forms, and we call these polymorphous (meaning many-forms).

DIAPHANEITY

Diaphaneity may be a tough word to spell, but it is an easy characteristic to remember about minerals. It is pretty much the way light will interact with the mineral; minerals can be translucent and transparent. The diaphaneity can single out many minerals for identification.

HARDNESS

Hardness is also a very indicative tool to identify a mineral, but be mindful that it is possible for different cleavage planes to provide a different hardness. This goes down to a molecular level; there is a scale for hardness known as the Moh's scale of hardness. I do much better learning when I can form mnemonics for memorization.  I use the following to remember the minerals correlated with the hardness scale. 

True Geologists Climb Faults And Observe Quarries To Contemplate Deformation.

Talc, Gypsum, Calcite, Fluorite, Apatite, Orthoclase, Quartz, Topaz, Corundum, Diamond

LUSTER

When you get to an introduction to geology class you will hear the instructor ask,"if a mineral was metallic or non-metallic?" This is a great tool for a quick dismissal of minerals in steps to identify minerals. Luster can be identified in many different ways because it is multi-faceted. You can have vitreous, adamantine, metallic, dull, greasy, pearly, resinous, silky, waxy, and etc.

SPECIFIC GRAVITY


Specific gravity is a great characteristic to identify many minerals. Galena is a fairly good one because of its specific gravity. It is basically how much the mineral weighs in comparison to water. Some minerals due to composition and structure will be much heavier than others that may take up the same volume of space. 

STREAK

Streak is used while scarifying a mineral against a "streak" plate, but I have used paper before when I have been out on the rig. This can help for identification as another tool to reinforce what you may believe a mineral is, in addition, to being able to identify minerals that may be similiar in appearance, but yield a different type and color of streak.

TENACITY


This is the reaction that the mineral will yield physical when under stress. The stress can come in several different ways whether it be bending, crushing, tearing, or breaking. Most minerals are brittle that you will come to find out, but other minerals can be flexible, malleable, ductile, sectile, and sometimes even elastic.