Lamproite
Ultrapotassic, volatile-rich ultramafic igneous rock
A rare ultrapotassic, magnesium-rich volcanic rock from deep in the mantle, famous as the diamond host at Argyle in Australia.
- Mohs hardness
- 5-6
- Color
- Dark grey to greenish or brownish-black
- Type
- igneous
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Overview
Lamproite is a rare, volatile-rich igneous rock that is both ultrapotassic (very high potassium) and rich in magnesium. It contains unusual minerals such as leucite, phlogopite mica, potassium-rich amphibole (richterite), and titanium-rich phases, reflecting an exotic deep-mantle source.
Lamproites are best known because some, like the Argyle pipe in Western Australia, are diamond-bearing, making them one of only two main rock types (with kimberlite) that bring diamonds to the surface. Named varieties include wyomingite, orendite, and madupite from the Leucite Hills of Wyoming.
They typically erupt as small pipes, dikes, and lava flows.
Formation & geology
Lamproite magmas originate by very low-degree melting of ancient, chemically enriched (metasomatized) mantle, often beneath thick, stable cratons. The melts are volatile-rich and ascend rapidly, erupting explosively to form diatreme pipes or quietly as small flows and dikes.
Diamond-bearing lamproites, like kimberlites, must rise fast enough from great depth to preserve diamonds. Classic localities include the Argyle and Ellendale fields in Western Australia and the Leucite Hills of Wyoming, USA.
How to identify it
Lamproite is a dark, fine-grained to porphyritic rock that may show shiny phlogopite mica flakes and, in fresh samples, leucite. It is typically heavy and dark grey-to-brownish, often altered.
Hardness is around 5-6. Lamproite is genuinely difficult to identify by eye and is usually confirmed by its distinctive ultrapotassic, magnesium-rich chemistry and rare mineral assemblage in the laboratory. Distinguish it from kimberlite and lamprophyre by mineral and chemical analysis, and from basalt by its exotic potassic mineralogy.
Uses & significance
Lamproite's overwhelming significance is as a diamond source rock: the Argyle lamproite was for decades the world's largest diamond producer and the main source of rare pink diamonds. As such, lamproite pipes are key exploration targets.
The rock itself has essentially no construction, gemstone, or metaphysical use; its value lies entirely in the diamonds it may carry and in what it reveals about deep mantle chemistry.
Frequently asked questions
Does lamproite contain diamonds?
Some lamproites do; the Argyle pipe in Western Australia was a famous diamond-bearing lamproite and a major source of pink diamonds.
How is lamproite different from kimberlite?
Both are deep, volatile-rich diamond hosts, but lamproite is ultrapotassic with minerals like leucite and richterite, whereas kimberlite is more carbonate- and olivine-rich.
What does ultrapotassic mean?
It means the rock has very high potassium relative to sodium and other elements, a hallmark of lamproite chemistry.
Where is lamproite found?
Notable occurrences include the Argyle and Ellendale fields of Western Australia and the Leucite Hills of Wyoming, USA.
Lamproite guides
In-depth guides for identifying, valuing, and understanding Lamproite.
