MINERAL IDENTIFICATION PROJECT

You've been out camping and picked up an unusual rock, someone brought back a stone carving from Mexico, or you've chosen Geology 101 as an elective.  You are now looking for a quick and painless way to identify minerals.  Well, you just found it!

There are few general parameters that define minerals.  First, minerals are a naturally occurring, relatively uniform, mix of elements that results in a stable definable solid.  Naturally occurring means that a geologic process such as evaporation, weathering, volcanic eruption, or burial at great depth created the conditions for mineral creation.  The mix of elements, or chemistry, is usually the defining property of a mineral and it over-rides most other properties.  Second, minerals (with few exceptions) are crystals.  Crystals are a highly organized assemblage of atoms whose internal organization is expressed by the development of external faces (facets) which are unique to each mineral.  Finally, the physical properties, such as chemistry, hardness, density, luster and color, are highly consistent from one sample to another.  This being said, minerals are from the earth, and are therefore a bit dirty in their chemistry and physical appearance.  Where one sample will have large well developed purple crystals another will be green and have crystals too small to distinguish--but both can be the same mineral!
 
The following is a brief description of the physical parameters used by this search engine to identifying mineral samples.

Hardness is the property of a mineral to resist abrasion.  Some minerals can be scratched easily while others are almost impossible to scratch.  Geologists developed a scale called the "Mohs Hardness Scale" based upon the hardness of various minerals, each with a different resistance to abrasion than other minerals in the scale.  The scale runs from talc at 1, a very soft mineral to diamond at 10, the hardest mineral.  Scratch the surface of your sample with one of the minerals from the Mohs kit and see if the surface is marked.  If not, use progressively harder minerals from the kit until it is marked.  This will be the hardness of your sample.  To provide for some uncertainty in the hardness measurement, this search engine displays all minerals with a .5 lower hardness to a 1.0 higher hardness than the number input.

Mohs Scale

Relative Scale

The density of a mineral is its mass per unit volume (g/cm³).  This is generally compared to an equal volume of water to come up with specific gravity (s.g.).  One could make this comparison by accurately weighing a mineral in grams and then sinking it in a graduated beaker of water where the initial depth and the subsequent depth are measured.  The mineral weight is then divided by the volume of water displaced in cm³.  Complex, but it can be done.  You can make a relative scale using sand and copper pennies.  You eyeball the volume of your sample and compare it to an equal volume of sand or pennies.  If your sample weighs less than the sand then it is less than 2.5 s.g., if more, then it's above 2.5 s.g.  If it takes twice as much sand to equal the weight of your sample then the sample is about 5 s.g.  If it's more than 5 s.g. use the pennies--they have a specific gravity of about 9.  This search engine takes into account some uncertainty in the s.g. of your sample, and it will select those minerals with approximately the same s.g. you input.

Cleavage is the property of a mineral to break along a definite plane or planes.  Mica is an example of a mineral with one perfect cleavage plane.  Table salt, halite, is an example of a mineral with 3 perfect planes of cleavage.  In looking through the references, you'll encounter various descriptions of cleavage such as perfect, good, fair, poor--it is a judgmental scale and not easily quantified.  This database uses the following descriptions for cleavage:

Cleavage

Fracture is the way a mineral breaks if it doesn't break along a cleavage plane.  Minerals such as quartz have smooth, curved fractures similar to a curved clam shell, other minerals break differently.  Minerals such as asbestos break into long fibrous or splintery fragments.  Like cleavage, the way something fractures is descriptive and variable.

Fracture

Luster is the property of the crystal surface to reflect light.  Some transparent to translucent minerals will have a glassy to adamantine (diamond like) reflection while other will have a waxy to dull reflection.  Some Opaque minerals will have a golden, coppery or silvery metallic luster.  Metallic luster is a definite indicator and should be used in the identification process.  The following descriptions are used in this database:

Luster

For some minerals, color is the defining property and a constant.  For others, color is the result of inclusions, impurities in the crystal structure, or the type of light available when viewing the sample.  Color is an important property and constant for minerals with a metallic luster, but in transparent to translucent minerals it isn't.  Finally on color, what is red to someone could be scarlet, pink or brick red to someone else--color is generally a subjective property.  Shades of color such as dark red, red and pink are grouped together in the red color selection.
Streak is the finely powdered trace a sample leaves when scraped across an unglazed ceramic plate.  Although the color of your sample might be variable the streak is generally constant and therefore more useful for mineral identification.

Given adequate space to fully develop, minerals are driven by their internal chemistry to form into various shapes.  These shapes can be short and squat, long and slender, needlelike, booklike or like grains of sand.  Each mineral is unique in the faces it develops and the way these surfaces grow.  The following descriptions of crystal shapes were used in the database:

Crystal Expression