Minerals & Rocks

There are thousands of minerals, and they come in all shapes and sizes. Minerals are classified based on 5 criteria; to be a mineral a substance must be solid under normal conditions, it must have a specific chemical composition, it must have a crystal structure, it must be in organic and naturally occurring (not man made).

Minerals can form in solutions or from cooling magma. Minerals in solutions can settle and crystallize in both hot and cold fluids. Evaporites are minerals formed when water evaporates and leaves the salt or mineral behind, such as Halite. Minerals forming from cooling magma are larger if the cooling process is very slow.

Minerals are best identified by hardness and chemical composition. Properties such as color can vary greatly in the same mineral due to impurities of the location where the mineral formed. Mohs Scale can be used to help identify common minerals. It ranks 10 minerals from softest to hardest and compares their hardness to common materials such as a fingernail, steel file, and glass crystal. The softest mineral on the scale is Talc, followed by Gypsum. The hardest mineral on the scale is Diamond. Based on how well a mineral resists being scratched, it is ranked on the scale. The softest minerals can be scratched by a fingernail while the hardest minerals can only be scratched by harder materials like iron or diamond. Many industrial drills are coated with diamond for higher strength and endurance.

Minerals are part of many products we use in addition to making beautiful jewelry. Fluorite is in toothpaste, Gypsum is in drywall, Calcite is in chalk, Hematite gives us iron, and Halite is salt. Glass is not a mineral because it does not have a crystal structure but it is made of silica sand. Ice is still a question on the table!

Other ways to identify minerals include Streak: the powder left behind when a mineral is scratched on a surface. Iron Pyrite (Fool's Gold) can be differentiated from real Gold through Streak because Pyrite leaves a greenish powder while Gold leaves a yellow powder. Minerals also have properties referring to their appearances. Luster is how a mineral reflects light, ex. Metallic, Glassy, Pearly, Greasy, Fibrous etc.

Rocks are made of minerals! Whether its a combination of several minerals that accumulated or mostly one mineral with some other substances, minerals make up all rocks. Most minerals are formed into sedimentary rock as weathering breaks down large samples into smaller sediments then recombines them over time. Heat and/or pressure can change the minerals within rock into new minerals and therefore new rock. If rock is made molten, it can mix and combine minerals into igneous rock. Any rock can become any other rock this way!

Sedimentary rock forms through the processes of compaction and cementation. After the natural elements of Earth wear down rocks on the surface into sediments, erosion and deposition accumulate the sediments, often in bodies of water. Over time, the layers of sediment on the bottom are compacted (pressed down and pressed together) by the weight of new sediment deposits above. Any mineral rich water is squeezed out of these lowest layers, leaving the minerals to cement the sediments together creating rock. Sedimentary rock often has visible, straight lines representing these layers by showing differing colors of sediment deposits. There are 3 types of Sedimentary rock: Clastic, Chemical, and Organic. Clastic rocks are what most people think of when they hear "sedimentary rock". They usually have visible layers and form through compaction. Chemical rocks are formed in mineral-rich solutions, usually in bodies of water that can evaporate. Organic rocks are those that contain organic materials, such as fossil remains of plants or animals.

Igneous rock forms through the processes of cooling and crystallization of magma. There are 2 categories of Igneous rock: Intrusive (Plutonic) and Extrusive (Volcanic). Intrusive igneous rocks are formed from magma trapped in the crust cooling very slowly. The mineral crystals grow large and visible in these rocks, such as Granite and Gabbro. Extrusive igneous rocks are formed from lava exiting volcanoes, cooling quickly due to exposure to the elements. These rocks have very small mineral crystals, often not visible to the naked eye, such as Obsidian or Basalt.

Metamorphic rocks are those that are placed under extreme pressure or close to intense heat, such as a body of magma in the crust. The pressure and heat can change the minerals within the rock, realigning them or forming new minerals altogether. The categories of Metamorphic rock are Foliated and Non-Foliated. Foliated rocks show signs of pressure as flattened minerals that look similar to broken bands, ex. Gneiss (from Granite). Non-Foliated rocks do not have banding, ex. Marble (from Limestone).