ELLENDALE LAMPROITE LAVA
Western Australia's Ellendale Lamproite Field contains
diamondiferous lamproite intrusions. What's more interesting, really,
from a volcanics point-of-view, is that lamproite lava (= extrusive
lamproite) is associated with some of the Ellendale lamproite bodies.
Lamproite lava is a rare rock type (ordinary intrusive lamproite pipes
themselves are not super-common either). The rock shown below is a
lamproite lava sample that's gorgeous in a way that the photos can't convey.
The unweathered matrix is light gray-brown, and the
large phenocrysts (black-looking or dark brown-looking or sparkly white in the
photos below) are wonderfully lustrous golden-brown phlogopite mica
crystals (ideally KMg3(Si3Al)O10(F,OH)2
- potassium-magnesium hydroxy-fluoro-aluminosilicate). Many of them
display well-defined hexagonal crystal structures. I'm not exactly sure
about the mineral content of the matrix - it possibly has titanate minerals
(having TiO3) or armalcolite ((Mg,Fe,Al)(Ti,Fe)2O5).
This rock comes from the Ellendale Center No. 5, a
subcommercially diamondiferous lamproite body in the Ellendale Lamproite Field
(northeastern margin of the Canning Basin, Kimberley, northern Western
Australia). This Ellendale lamproite lava is Early Miocene in age (19-22
m.y.).
Phlogopite leucite lamproite lava (field of view ~7.5 cm across) from the Ellendale
Center No. 5 (Lower Miocene, 19-22 m.y.), Western Australia.
Phlogopite leucite lamproite lava (field of view ~3.5 cm across) from the Ellendale
Center No. 5 (Lower Miocene, 19-22 m.y.), Western Australia.
Most info. provided by Tony Peterson.