Brecciated Red Jasper Crystals
Highly polished, brecciated Red Jasper tumbled stones from South Africa.
Stone described as brecciated is made up of large angular fragments of pre-existing rocks and minerals. The particles, which are usually larger than two millimetres, are correctly known as clasts. A clast is a fragment of rock.
The spaces between the clasts are filled with smaller particles bound together with a mineral cement. The distinctive angular fragments often make brecciated rocks relatively easy to identify.
Although mostly sedimentary, brecciated rocks can also be igneous or metamorphic. The formation of sedimentary brecciated rock begins when sediments accumulate to form one large mass. As the size of the mass increases, the sediment at the bottom becomes buried. The increased pressure reduces the amount of space between the sediments.
Groundwater is gradually squeezed out, leaving only the minerals behind. These minerals form a kind of cement that binds the fragments together. Quartz, calcite and iron oxides are the most common types of cement.
Jasper is a mixture of different types of microcrystalline quartz with various impurities of other minerals.
In brecciated Jasper, cracks that repeatedly open in the rock, usually due to tectonic activity, tend to be filled with more Jasper.
The deep reddish-brown colour of these brecciated Red Jasper crystals is from hematite.
These tumbled stones are large, although size can vary from piece to piece.
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