Rocksday

Chalk

A soft, white limestone made of trillions of microscopic plates shed by ocean algae.

Chalk specimen
Photo: Nessa Eull, CC0, via Wikimedia Commons

How to identify chalk

  • Bright white and powdery.
  • Leaves white marks on hands and surfaces.
  • Fizzes in acid.
  • Very light and porous.

Often confused with

Where it's found

  • White Cliffs of Dover, England
  • Champagne, France
  • Monument Rocks, Kansas

Uses

Lime, cement and fertilizer.

Rock tumbling

Not suitable for tumbling.

Did you know?

The Cretaceous period is named after Latin creta, 'chalk'. Today's classroom chalk is mostly gypsum.

Think you could spot it from a blurry close-up?

Play today's Rocksday