What do minerals look like

As you can see, diamond is a 10 on Mohs Scale. Diamond is the hardest mineral, which means that no other mineral can scratch a diamond. Quartz is a 7, so it can be scratched by topaz, corundum, and diamond. Quartz will scratch minerals, such as fluorite, that have a lower number on the scale.

Suppose you tested a piece of pure gold for hardness. Calcite would scratch the gold, but gypsum would not because gypsum is a 2 and calcite is a 3. That would mean gold is between the hardness of gypsum and calcite, or 2. A hardness of 2. It is only about as hard as your fingernail. Read about Mineral hardness. Read about Luster here. Color is probably the easiest property to observe. Unfortunately, you can rarely identify a mineral only by its color.

One of the most important physical properties of minerals, reflecting the nature of the interaction of the electromagnetic radiation of the visible region with the electrons of the atoms, molecules, and ions of the crystals and with the electron system of the crystal as a whole. In mineralogy, color is one of the primary diagnostic properties of natural compounds, of great importance in geological prospecting for the identification of minerals.

The color of gems and semiprecious stones is one of their main qualitative gem characteristics. Three main groups of minerals are identified on the basis of the property of color: idiochromatic, allochromatic, and pseudochro-matic.

Idiochromatic minerals are "self colored" due to their composition. The color is a constant and predictable component of the mineral.

Examples are blue Azurite, red Cinnabar, and green Malachite. Allochromatic minerals are "other colored" due to trace impurities in their composition or defects in their structure. In this case, the color is a variable and unpredictable property of the mineral.

Examples are the blue in Amazonite orthoclase , yellow in Heliodor spodumene and the rose in rose quartz. Pseudochromatic minerals are "false colored" due to tricks in light diffraction.

In these cases, color is variable but a unique property of the mineral. Examples are the colors produced by precious opal and the shiller reflections of labradorite. Read about Color of Minerals. Streak is the color of the powder of a mineral. Metallic minerals are also always opaque. Non-metallic minerals may be shiny and reflect light, however, they do not look like a metal. Surface color may be helpful in identifying minerals, although it can be quite variable even within a single mineral family.

Mineral colors are affected by the main elements present, but also by impurities, inclusions, and defects in the crystal structure. Pressure and temperature conditions can also affect mineral color. Using the mineral quartz for example, in its purest form SiO 2 , it will be clear. However, impurities by trace amounts of iron can change the color from purple amethyst to yellow citrine or pink rose quartz ; tiny inclusions of the titanium mineral rutile can give quartz a blue color, and exposure to natural radiation within the crust can provide a grey smoky color.

Pure quartz SiO2 is the clear sample on the left-hand side; followed by smoky quartz, rose quartz, and amethyst quartz. Each of the colored quartz samples contains an impurity in the chemistry. CC BY Attribution 3. There are some minerals that predominantly show a single color. All of these minerals have a predictable range of colors due to element substitution within their crystalline structures.

Feldspar colors including pink, white, green, gray and others. With notable exceptions, color is usually not a reliable diagnostic property of minerals. For identifying many minerals, a more reliable indicator is streak, which is the color of the powdered mineral. Streak examines the color of a powdered mineral, and can be seen when a mineral sample is scratched or scraped on an unglazed porcelain streak plate. A paper page in a field notebook may also be used for the streak of some minerals.

Minerals that are harder than the streak plate or the paper will not show streak, but will scratch the porcelain and tear the paper! For these minerals, a streak test can be obtained by powdering the mineral with a hammer and smearing the powder across a streak plate or notebook paper.

Note the absence of a mineral streak via this method is also a useful observation to record. While mineral surface colors and appearances may vary, their streak colors can be diagnostically useful. An example of this property is seen in the iron-oxide mineral hematite. Hematite occurs in a variety of forms, colors and lusters, from shiny metallic silver to earthy red-brown, and different physical appearances.

Imagine you have an unknown mineral. You find that it can scratch fluorite or even apatite, but feldspar scratches it. Note that no other mineral can scratch diamond. Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways.

Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite breaks between layers of sodium and chlorine to form cubes with smooth surfaces Figure below. One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral.

Minerals may have characteristic fractures Figure below. Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. Some minerals have other unique properties, some of which are listed in Table below. Hint: It is most likely found on your dinner table. Skip to main content. Search for:. Mineral Identification Lesson Objectives Explain how minerals are identified.

Describe how color, luster, and streak are used to identify minerals. Explain how the hardness of a mineral is measured.