What is Selenite?

Selenite is a naturally occurring crystalline mineral also known as gypsum or calcium sulfate. Despite the similarity in the words, selenite contains no significant amount of selenium. In its purest form, selenite is nearly transparent and colorless; however most mined selenite is whitish to opaque to brownish in color. EcoGEM’s deposit is a bright white, and is one of the purest on earth. Gypsum is also available as an industrial by-product from power plants and citric, lactic and phosphoric acid plants which use calcium carbonate to neutralize emissions of sulfur-containing stack gases. Byproduct gypsum is not allowed to be used for organic farming.

In nature, selenite is formed as an evaporative mineral, located in former alkaline lake muds, evaporated seas, salt flats or caves. Selenite (or gypsum) is hydrated calcium sulfate with each molecule containing two molecules of water. The anhydrite form may also occur naturally, if it is buried deep in the mineral deposit and not exposed to air. It does not contain water. However when exposed to the atmosphere, the anhydrite picks up water and converts to the hydrate form.

Calcium sulfate contains about 24% calcium and 18% sulfur. However, the mineral or by-product will vary in quality and may contain from 17 to 23% calcium and 14 to 18% sulfur along with some magnesium (less than 1%), calcium carbonate (lime) and other minerals and metals.

Selenite’s most common use is in the production of wall board. Increasingly, selenite is recognized as a soil amendment and fertilizer in agriculture. Six key benefits include:

1. Selenite is a source of calcium and sulfur for plant and soil nutrition. This is important because all plants need calcium and sulfur to grow. Both occur naturally in soils, but may not be present in sufficient quantities or may be chemically unavailable. Calcium in soil is tied up with carbonate and soil is becoming more deficient in sulfur. Selenite is a natural source of these two important nutrients.

2. While selenite doesn’t lower or raise soil pH like lime does, it can reduce aluminum toxicity which is often found in acid subsoil. Calcium sulfate dissolves and leaches down in the soil displacing the aluminum that is toxic to root growth.

3. As an amendment selenite is best known for its ability to improve soil structure. Calcium helps flocculate or aggregate soil particles together into natural peds which improves porosity and aeration and remediates deflocculation of sodic soils.

4. It can remediate high levels of sodium in irrigation water. Sodium deflocculates the soil. Calcium can displace sodium on soil particles so it can leach out of the root zone.

5. Selenite improves structure and increases water holding capacity and infiltration. Soils drain better and are less prone to ponding and saturation. It also reduces surface crusting that can impede infiltration as well as reduce seedling emergence.

6. Lastly it can reduce runoff and erosion. Better structure means greater infiltration and less soil and phosphorus runoff.

In the last century, farmers discovered that applying nitrogen, potassium and phosphorous-containing fertilizers improved crop yield and enabled them to feed the earth’s growing population. In this century, farmers who use selenite will be on the forefront of the next wave of productivity improvements.

Author: Dr. Daniel Davidson

Dr. Daniel Davidson – EcoGEM Agronomist. Dr. Daniel Davidson is a nationally recognized agronomist. He served most recently as Director of Strategic Research for the Illinois Soybean Association. Dr. Davidson has also served in various capacities at GEOSYS, Cargill, Agri Business Group and Agri Growth, Inc. He holds a Ph.D. in Agronomy from Washington State University and an MS in Agronomy from the University of Missouri.