Rocksday

Jarosite

A yellow-brown iron sulfate formed where sulfide minerals weather in acidic water.

Jarosite specimen
Photo: Dave Dyet http://www.shutterstone.com http://www.dyet.com, Public domain, via Wikimedia Commons

How to identify jarosite

  • Mustard-yellow to brown crusts of tiny crystals.
  • Pale yellow streak.
  • Often with weathered pyrite.

Often confused with

Where it's found

  • Barranco Jaroso, Spain
  • Utah
  • Mars

Uses

A clue to past acidic water, on Earth and Mars.

Rock tumbling

Not suitable for tumbling.

Did you know?

NASA's Opportunity rover found jarosite on Mars — evidence of ancient water.

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

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