Mini Me Geology Blog

Salt is a common evaporite mineral that exists around the world and is often called halite or rock salt. The mineral is very soft in relation to other minerals and can form nice crystal shapes. The crystals can form individually or in crystalline masses. Rock salt forms as a common sedimentary deposit in areas of enclosed salt water. Teachers and home school parents can use halite samples to teach children about a useful mineral that has easily identifiable physical and chemical properties. Many home experiments involving salt are easy to perform so that children have fun experimenting and learning simultaneously.

Chemical Composition and Physical Properties of Salt
Rock salt is composed of the mineral halite. The name halite comes from the Greek word for salt. The halite mineral is sodium chloride, or NaCl. Geologic samples of halite and rock salt are usually white to clear in color but can also be blue, pink, yellow, red and purple. On the Mohs Hardness Scale of 1 to 10, halite is a 2.5, which means it is a very soft mineral that is approximately the same hardness as your fingernail. You can scratch salt with a copper penny, pocketknife or steel file. Halite forms good crystal shapes with cubic cleavage, which means that the crystals naturally break into perfect cubes. The crystals may also form as a mass of interwoven cubes in a single deposit. Halite / rock salt crystals have a glassy luster, white streak and are salty to taste.

Halite Formation and Salt Domes
Halite forms in beds from the evaporation of salt water. These beds are large areas that formerly contained enclosed salt water such as lakes or seawater. As the salt water evaporates, the halite precipitates out of solution forming layered beds of salt crystals. These evaporite beds may stay at the land surface or other rock layers may deposit on top and bury the salt over time. Buried salt beds can eventually form underground salt domes. The salt beds are very malleable and lighter than most other rocks. When a crack is present in a rock mass above a salt bed, the layer of salt will rise through the crack forming dome shape underground.

Salt Locations Around the World
Halite occurs in deposits worldwide. Some of the most outstanding foreign locations for salt beds and crystals are in Antarctica, South America, Africa, Australia, Japan, China, Poland, Russia, Iran, Germany, the United Kingdom, Switzerland, Ireland, Finland, Poland, Morocco and Canada. In the United States, thick rock salt beds are located in New York State and extend westward through Ontairo, Canada and to the Michigan Basin. Large deposits of salt are also present in the Salina Formation beneath Cleveland, Ohio, and at locations in California, Arizona and New Mexico. Salt domes, often associated with oil deposits, appear in the regions along the Gulf Coast of Louisiana and Texas as well as areas in Germany, Spain and Iran among others.  

Common Uses for the Halite Mineral
Halite has many uses and is important to the chemical industry. The sodium and chloride in the rock salt crystals are sources for the production of hydrochloric acid, chlorine, soaps, caustic soda, sodium hydroxide and ceramic glazes. Salt is also a seasoning in food for people and animals. Rock salt is a good preservative for food and animal hides and is used to melt ice from roads in the winter months.

Teaching Geology with Salt
Salt is a fantastic teaching tool to help children understand the properties of minerals and how to identify a sample by testing the streak, hardness, luster, cleavage and color. You can also perform hands-on experiments to show children how to identify a mineral using tools such as hand lenses, streak plates and a geologic hammer. Have some fun with crystal cleavage by using a hammer to strike a halite or rock salt crystal and watch it break into smaller and smaller cubes! Classrooms and homeschool students can use halite and rock salt samples from our My Rockin’ Collection deluxe and junior minerals kit, or our Crystal Experiments Rock Detectives Kits.

Use our salt growing experiment to teach kids how salt crystals form from a solution of salt water. Another version of the experiment is to make a salt solution, pour it into a shallow dish and allow the water to evaporate leaving the salt in the dish.
If you have questions about halite and rock salt, email us!

Filed under: Geology / Earth Science, Minerals & Crystals on June 17th, 2011