Rocks to Avoid in a Terrarium

When setting up a terrarium, it’s crucial to avoid certain types of rocks that could be harmful to the plants and animals. Some rocks can alter the pH and chemistry of the soil or water, while others may have sharp edges or contain toxic minerals. Here are rocks to avoid in terrariums:

1. Limestone

  • Issues: Limestone is composed mainly of calcium carbonate, which can raise the pH of the soil or water, making it alkaline.
  • Impact: This can be harmful to plants and animals that require neutral or acidic conditions.

2. Marble

  • Issues: Similar to limestone, marble is also made of calcium carbonate and can affect the pH balance of the terrarium.
  • Impact: It can make the environment too alkaline, which is unsuitable for most terrarium inhabitants.

3. Sandstone (in aquariums)

  • Issues: While sandstone is generally safe for dry terrariums, it can disintegrate and alter the water chemistry if used in aquariums.
  • Impact: This can lead to water quality issues and potentially harm aquatic life.

4. Chalk

  • Issues: Chalk is another form of calcium carbonate and can severely alter the pH levels.
  • Impact: It can quickly make the environment too alkaline for plants and animals that thrive in more neutral conditions.

5. Soft Rocks

  • Examples: Gypsum and talc.
  • Issues: These rocks are too soft and can break down easily, altering the substrate and water chemistry.
  • Impact: They can make the environment unstable and unsuitable for most terrarium life.

6. Rocks with High Metal Content

  • Examples: Pyrite (fool’s gold), galena, and any rocks with visible metallic veins.
  • Issues: These rocks can leach heavy metals into the soil or water.
  • Impact: Heavy metals can be toxic to both plants and animals, causing health issues or death.

7. Rocks with Sharp Edges

  • Examples: Broken glassy rocks, some types of slate.
  • Issues: Sharp edges can injure animals or damage plant roots.
  • Impact: Can cause physical harm and stress to terrarium inhabitants.

8. Dyed or Painted Rocks

  • Issues: Artificially colored rocks can leach dyes and chemicals into the terrarium environment.
  • Impact: These chemicals can be toxic to plants and animals, affecting their health and well-being.

Safety Testing for Rocks

Before placing any rock in your terrarium, you can perform simple tests to ensure their suitability:

  1. Vinegar Test: Apply a few drops of vinegar to the rock. If it fizzes, the rock contains calcium carbonate and is unsuitable for terrariums that require stable pH.
  2. Water Soak Test: Soak the rock in water for a few days and test the water pH before and after. Significant changes in pH indicate that the rock is affecting the water chemistry.

General Tips

  • Research: Ensure you know the composition of the rock before adding it to your terrarium.
  • Source: Obtain rocks from reputable sources rather than collecting them from unknown environments, as this can introduce unwanted contaminants.
  • Inspection: Always inspect rocks for potential hazards, including sharp edges and signs of metal content.

By avoiding these types of rocks, you can help ensure a stable, healthy, and safe environment for your terrarium’s plants and animals.

See Safe Rocks to use