Properties of Minerals Geologists use characteristics to tell one mineral from another

Mineral Properties we will study Luster Hardness Cleavage Streak

Luster Refers to the way light reflects from the surface of the mineral. There are two types of luster, Metallic: looks like polished metal. Nonmetallic: does not look like polished metal. Nonmetallic can be shiny or dull.

Pyrite has metallic luster

Quartz has nonmetallic luster

Hardness Is measured by how easy it is to scratch. Geologists order the hardness by… Scratched by a fingernail. Scratched by a penny. Scratched by a nail. Scratched by a diamond. These are not all of the tools geologists use, but it will work for our experiment.

Gypsum is soft, it can be scratched by a fingernail.

Calcite is soft, but a little harder because it cannot be scratched by a fingernail, but it can be scratched by a penny.

Fluorite is harder. It can be scratched by a nail, but not a penny or fingernail.

Diamonds are the hardest mineral, so it scratches every mineral.

Cleavage Not all minerals have cleavage. Some minerals split easily along a flat surface. The number of lines that are created when a mineral is split will be the number of cleavage lines.

Mica has cleavage in one direction. It breaks along one line.

Feldspar has two lines of cleavage. It breaks along two lines.

Streak Red chalk on a chalk board makes red marks. White chalk makes white marks. Not all minerals work this way. When some minerals are scratched along a ceramic streak plate, it creates a different color.

Gold When gold is run across a streak plate it makes a yellowish-gold color. That makes sense.

Pyrite or “Fool’s Gold” When pyrite is run across a streak plate, it has a black or dark green streak. Pyrite is not worth much money, while gold is worth a lot. They look alike, so miners call it fool’s gold.

Hematite Hematite’s color is grey, but its streak is red. Hema means blood. The mineral was named hematite because it looked like it was bleeding when it was taken across a streak plate.

One mineral property we will not use… COLOR

A mineral can be many different colors. Below is Mica.

Many minerals can be the same color. Below are gold colored minerals Many minerals can be the same color. Below are gold colored minerals. Which one is gold?

None of them were real gold. The answer… None of them were real gold.

Just like with people… Outside color does not tell you much about the important characteristics.