How to Grow a Cup of Quick Crystal Needles

Simple Epsom Salt Crystal Spikes

view of glass with crystal needles

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Grow a cupful of Epsom salt crystal needles in your refrigerator. It's quick, easy, and safe.

Difficulty: Easy

Time Required: 3 hours


  • cup or small bowl
  • epsom salt
  • hot tap water

What You Do

  1. In a cup or small, deep bowl, mix 1/2 cup of Epsom salts (magnesium sulfate) with 1/2 cup of hot tap water (hot as it will get from the faucet).
  2. Stir about a minute to dissolve the Epsom salts. There will still be some undissolved crystals at the bottom.
  3. Place the cup in the refrigerator. The bowl will fill with needle-like crystals within three hours.
Magnesium sulfate crystals
Magnesium sulfate crystals readily take up dye, such as food coloring. Copyright (c) by Dai Haruki. All Rights Reserved. / Getty Images

Tips for Success

  1. Don't use boiling water to prepare your solution. You will still get crystals, but they will be more threadlike and less interesting. The temperature of the water helps control the concentration of the solution.
  2. If you like, you can place a small object at the bottom of the cup to make it easier to remove your crystals, such as a quarter or plastic bottle cap. Otherwise, carefully scoop the crystal needles from the solution if you wish to examine them or save them.
  3. Don't drink the crystal liquid. It's not toxic, but it's not good for you either.

Learn About Epsomite

The name of the crystal grown in this project is epsomite. It consists of hydrated magnesium sulfate with the formula MgSO4·7H2O. The needle-like crystals of this sulfate mineral are orthorhombic as Epsom salt, but the mineral readily absorbs and loses water, so it may spontaneously switch to the monoclinic structure as a hexahydrate.

Epsomite is found on the walls of limestone caverns. The crystals also grow on mine walls and timbers, around volcanic fumaroles, and rarely as sheets or beds from evaporation. While the crystals grown in this project are needles or spikes, the crystals also form fibrous sheets in nature. The pure mineral is colorless or white, but impurities may give it a gray, pink, or green color. It gets its name for Epsom in Surrey, England, which is where it was first described in 1806.

Epsom salt crystals are very soft, with a Moh scale hardness around 2.0 to 2.5. Because it is so soft and because it hydrates and rehydrates in the air, this is not an ideal crystal for preservation. If you want to keep Epsom salt crystals, the best choice is to leave it in a liquid solution. Once the crystals have grown, seal the container so no more water can evaporate. You can observe the crystals over time and watch them dissolve and reform.

Magnesium sulfate is used in agriculture and pharmaceuticals. The crystals may be added to water as bath salts or as a soak to relieve sore muscles. Crystals may also be mixed in with soil to help improve its quality. The salt corrects magnesium or sulfur deficiency and is most often applied to roses, citrus trees, and potted plants.

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Your Citation
Helmenstine, Anne Marie, Ph.D. "How to Grow a Cup of Quick Crystal Needles." ThoughtCo, Apr. 5, 2023, Helmenstine, Anne Marie, Ph.D. (2023, April 5). How to Grow a Cup of Quick Crystal Needles. Retrieved from Helmenstine, Anne Marie, Ph.D. "How to Grow a Cup of Quick Crystal Needles." ThoughtCo. (accessed June 7, 2023).