Identifying Minerals Chapter 9.2

Characteristics of Minerals 1. Characteristics of Minerals a. A mineralogist is a scientist who specializes in the study of minerals. b. Every mineral has a set of specific properties that can used to identify that mineral. i. These properties are the result of the minerals chemical composition.

Properties of Minerals c. Properties of minerals can be identified by simply looking at the mineral or by performing a test. These properties include… i. Color ii. Luster iii. Streak iv. Cleavage v. Fracture vi. Hardness vii. Crystal Shape viii. Density

Color b. Color is a simple property that can be used to identify a mineral. i. While in some cases color is reliable, in most cases it is not. ii. The color of a mineral can be changed by a slight change in chemical composition. iii. Color is also unreliable because weathered surfaces may hide the color of the mineral.

Colorful Minerals

Luster c. Luster is light reflected from the surface of a mineral. Basically, the shine of the mineral. i. Minerals that reflect light like polished metal are said to have a metallic luster. ii. All other minerals have a nonmetallic luster. iii. Other ways to categorize luster are glassy, waxy, pearly, brilliant, and dull luster.

Luster

Streak d. Streak is the color of a mineral in powdered form. i. The easiest way to observe this property is rub the mineral against a streak plate, or against a piece of unglazed ceramic tile. ii. The streak may not be the same color of the large piece of the mineral. iii. Metallic minerals generally have a dark to black streak, while nonmetallic minerals generally have a light shade of the mineral to colorless streak.

Streak

Cleavage e. Cleavage is the tendency for minerals to split along a certain surface. i. This property is due to the type of bonds in the internal structure of the mineral. 1. For example, mica tends to break into sheets, while galena tends to break into small cubes because of the three cleavage directions that are at right angles to each other.

Cleavage

Fracture f. A fracture is when a mineral breaks into uneven or curved pieces. i. A fracture is categorized by its appearance. ii. A rough surface is called uneven or irregular. iii. A broken surface that looks like broken wood is called splintery or fibrous. iv. A curved surface is called conchoidal.

Fracture

Hardness a. Hardness is the measure of the ability of a mineral to resist scratching. i. Hardness can be determined by scratching it against the minerals on the Mohs Hardness Scale. 1. This scale lists 10 minerals in order of increasing hardness, with talc being a 1 and diamond being a 10.

Hardness 2. In order to determine the hardness of a specific mineral, you must determine which mineral is the hardest mineral on the scale it can scratch. 3. If you come across a mineral that doesn’t scratch another and is not scratched by the test mineral, then the hardness is equal.

Hardness

Crystals a. Mineral crystals will always form in one of six basic shapes. A certain mineral always has the same general shape because the atoms or ions that form its crystals always combine in the same geometric pattern.

Crystal Shape

Density a. The density of a mineral can be calculated by comparing the ratio of the mass of a mineral to its volume. i. D=m/V ii. A more dense mineral will feel heavier than a less dense mineral of the same size.

Special Properties 1. Special Properties of Some Minerals a. Magnetism is an identifiable property that can be easily tested by passing a magnet past a mineral to see if it is attracted to it. b. Fluorescence is the ability of a mineral to glow under ultraviolet light. c. Phosphorescence is the ability of a mineral to continue glowing after the ultraviolet light has been removed.

Fluorescence & Phosphorescence

Special Properties d. Refraction is the bending of light through a substance. i. Double refraction is the ability of a mineral to produce two images of any object when viewed through them.

Double Refraction

Special Properties d. Radioactivity is the unstable arrangements of protons and neutrons in the nucleus of an atom. Examples of radioactive elements include uranium and radium which occur in some minerals such as carnotite, uraninite, and autunite.

Radioactive Minerals