Madupite Identification Guide
A guide to identifying Madupite, a rare potassium-rich lamproite, by its dark glassy groundmass and phlogopite-diopside content.
Read the full Madupite encyclopedia entry →
What Madupite Looks Like
Madupite is a very rare, dark volcanic rock — a potassium-rich lamproite. It is a fine-grained to glassy ultrapotassic igneous rock famous from the Leucite Hills of Wyoming.
- Color: dark gray to black, dull
- Luster: dull to slightly glassy groundmass
- Texture: fine-grained/porphyritic with phenocrysts of diopside and phlogopite mica set in a glassy K-rich groundmass (madupitic texture)
- Key minerals: diopside, phlogopite mica, perovskite, apatite, in a glassy alkali-rich matrix
Step-by-Step Field ID Checklist
- Note the dark, dense, fine-grained look of a mafic-to-ultramafic volcanic rock.
- Look for shiny bronze-brown mica (phlogopite) flecks scattered in the dark matrix.
- Spot small green diopside crystals as phenocrysts.
- Confirm a glassy or felted groundmass rather than coarse interlocking crystals.
- Test hardness — pyroxene/mica around 5.5-6; the rock is hard overall but mica peels.
Key Diagnostic Tests
- Mohs hardness: ~5.5-6 (diopside), mica softer (~2.5-3).
- Texture: "madupitic" — phenocrysts in a glassy poikilitic groundmass — is diagnostic among lamproites.
- Acid: no reaction.
- Density: relatively high for a volcanic rock (mafic mineralogy).
- Field association: occurs with leucite-bearing volcanic rocks.
Common Look-Alikes and How to Tell Them Apart
- Basalt: also dark and fine-grained, but basalt is plagioclase + pyroxene, lacking abundant phlogopite and the K-rich glassy groundmass.
- Other lamproites (e.g., orendite, wyomingite): closely related; madupite is distinguished by its glassy groundmass and madupitic texture versus more crystalline groundmass in wyomingite.
- Kimberlite: carries mantle xenoliths/olivine macrocrysts and is more serpentinized; madupite lacks the typical kimberlitic blue-ground look.
- Lamprophyre: similar dark porphyritic look but different mineralogy; lab petrography is often needed.
Where It Is Typically Found
Madupite is classic from the Leucite Hills volcanic field, Sweetwater County, Wyoming, USA — one of the world's best-known ultrapotassic lamproite provinces. It is rare elsewhere.
Frequently asked questions
What is Madupite?
Madupite is a rare, dark, potassium-rich lamproite — an ultrapotassic volcanic rock with diopside and phlogopite phenocrysts in a glassy K-rich groundmass, classic from the Leucite Hills of Wyoming.
How do you identify Madupite?
Look for a dark, fine-grained volcanic rock with bronze-brown phlogopite mica flecks and small green diopside crystals set in a glassy groundmass (madupitic texture). Field association with leucite rocks helps.
Madupite vs basalt?
Both are dark and fine-grained, but basalt is built of plagioclase and pyroxene, while madupite is ultrapotassic with abundant phlogopite mica and a glassy K-rich matrix and no plagioclase.
Where is Madupite found?
It is best known from the Leucite Hills volcanic field in Sweetwater County, Wyoming, USA, and is rare elsewhere in the world.