Pumice

Pumice is a light, porous volcanic rock that consists of highly vesicular rough textured volcanic glass. It is created when super-heated, highly pressurized rock is violently ejected from a volcano.

Description of what it is like

• Appearance: Light colored (white, cream, grey) rock full of tiny holes (vesicles).
• Texture: Rough, scratchy, and sponge-like.
• Properties: Extremely lightweight; dry pumice will float on water. It is abrasive but friable (crumbles under pressure).

Origin and where to find it

• Occurrence: Volcanic regions.
• Location: Near stratovolcanoes or washing up on beaches after ocean eruptions.
• Recognition: It looks like a hard sponge and floats.

Minimum processing required

1. Collection: Gathering loose stones.
2. Washing: Rinsing off salt or dirt.
3. Crushing: Pounding into powder if used as a fine abrasive.
4. Shaping: Can be rubbed against harder stones to shape into blocks.

Tools needed to work on it

• Hammer: To crush it.
• Mortar and Pestle: To grind it into fine powder.

Common forms of use

• Solid Block: Used to scrub skin (calluses) or scour cookware.
• Powder: Used as a polishing agent for Glass, metal, wood, or Bone.
• Aggregate: Mixed with Cement to make lightweight concrete (used by Romans in the Pantheon dome).

Possible substitutes

• Sand: Coarser abrasive.
• Sandstone: Harder abrasive block.
• Ash: For cleaning.
• Steel Wool: Modern abrasive.

Limitations and common failures

• Crushing: It is not structural on its own; it crushes easily.
• Absorption: Absorbs water eventually and will sink.

Risks and safety

• Dust: Breathing volcanic glass dust is bad for lungs.
• Abrasion: Can scratch softer materials unintentionally.

Related materials

• Obsidian: Volcanic glass without the bubbles.
• Ash: Fine volcanic particles.
• Scoria: A darker, heavier, denser volcanic rock (sinks).