|Rounded fragments are held by a cementing matrix|
Sunday, April 4, 2010
Brecciated Silver Ore from the Alma District
One of our our study members found this unsual ore specimen that reveals brecciation. Note the small, rounded clasts.
Breccia is a rock composed of fragments of minerals or rocks in a matrix (cementing material). The fragments in this specimen are different from the composition of the matrix. This may be a hydrothermal breccia. This type of breccia is formed in a void along a fault underground. The void draws in hot water that violently boils--like an underground geyser. Rock at sides of the fault fall inwards and the broken rock gets caught up in a churning mixture of rock, steam and boiling water. The rock fragments hit each other and sides of the fault which quickly rounds the once angular breccia. fragments.