Rocksday

Lamprophyre

Lamprophyre is an igneous rock with a Mohs hardness of about 5–6 and a sparkling luster, usually black, gray, green or brown.

A dark dike rock whose large crystals are mica or amphibole, not feldspar.

Lamprophyre specimen
Photo: Pelex, CC BY 3.0, via Wikimedia Commons

How to identify lamprophyre

  • Dark, with shiny black or brown flakes or needles in a fine matrix.
  • Occurs as thin dikes cutting other rocks.
  • The big crystals are biotite, phlogopite or amphibole.

Often confused with

Where it's found

  • Vosges, France
  • Lake District, England
  • Navajo volcanic field, Arizona

Uses

Rarely quarried. Studied because some gold districts have lamprophyre dikes nearby.

Rock tumbling

Can be tumbled with care.

Did you know?

Unlike most porphyries, the crystals you notice first are mica or amphibole.

Lamprophyre FAQ

What is lamprophyre?

Lamprophyre is an igneous rock with a Mohs hardness of about 5–6 and a sparkling luster, usually black, gray, green or brown. A dark dike rock whose large crystals are mica or amphibole, not feldspar.

How do you identify lamprophyre?

Dark, with shiny black or brown flakes or needles in a fine matrix. Occurs as thin dikes cutting other rocks. The big crystals are biotite, phlogopite or amphibole.

How hard is lamprophyre?

Lamprophyre has a Mohs hardness of about 5–6. Its hardness varies from 5 to 6, so scratch tests depend on the piece.

Where is lamprophyre found?

Notable localities include Vosges, France; Lake District, England; and Navajo volcanic field, Arizona.

What is lamprophyre used for?

Rarely quarried. Studied because some gold districts have lamprophyre dikes nearby.

Can you tumble lamprophyre?

Yes, with care.

What is lamprophyre often confused with?

Lamprophyre is most often confused with Basalt and Diabase. Basalt's crystals, if any, are usually pale feldspar or green olivine, not big mica books. Diabase is a salt-and-pepper of feldspar laths and pyroxene.

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