What rocks are opals found in?
Opals are found in sedimentary rocks, the most common is clay stone. Claystone made of is layers of clay compacted together overtime. Opals can also be found in sandstone. Opals are most commonly found; in areas of claystone near faults (large cracks), blows (areas with fractured or broken rocks) and joins (small cracks in rocks).
|
Rocks found near by
In mining there are often multiply layers of different types of rock. Around clay stone usually sand stone can be found. Sandstone is a sedimentary rock alike claystone, this is one of the reasons they are often found together. Sand stone is formed in sandy areas and has a sandy texture it is generally crumbly and easy to drill through. Sandstone is often formed near beach or coastal areas, But in cases like Lightning Ridge it is formed by red sand.
|
This is and example of the layering and orange coloured sandstone, The whiter colour clay stone with opal laced through it.
|
why are opals found in Clay stone?
Opals were
formed many centuries ago in a time period called tertiary period. During this
time the clay stone and sand stone had a lot of weathering. Over time silica
(what opals are made of) was filtered from the sandstone layers of rock by the
weathering and water. The silica passed through rock until it was trapped by clay stone. From here over time it formed opals.
- Once Clay stone is fully formed it is nearly impenetrable for silica .
-Opals tend to be found in faults (weak points) this is because when the silica was filtering through rocks and it found the easiest path, weak spots.
-Opals tend to be found in faults (weak points) this is because when the silica was filtering through rocks and it found the easiest path, weak spots.
More about clay stone
Clay stone is a sedimentary rock. As its name suggests it is formed of clay. Over time many small pieces of clay are compacted together to make clay stone. Because it is a more solid and heavy rock it takes longer to erode and doesn't pass through as many cycles as other rocks. Clay stone is a shiny rock, when broken it looks slightly like glass and tends to break into chips. It is sometimes confused with Mud stone and mud shale.