Author Marco Campos Venuti has just written a new book titled Genesis and Classification of Agates and Jaspers - a New theory. The Author is a PhD volcanologist and author of the Gemmologica Italiana.
Below is just summary of the information contained in this book.
The formation of various kinds of silica like Agates, Jaspers and Chalcedonies has been concluded that they originated from the influences of the weather, the dry, hot or the wet and the dry seasons, and sometimes meteoric impact into the earth and the environment.
It is known that Jasper belongs to the family of quartz which contains silica and has an opaque look. Jewellers and people who do lapidary work know that Jaspers do polish very well, however it can sometimes show some inclusions because it is porous.
Ocean Jaspers are the most common and are found deep in the seafloor which have been formed by sedimentation. In this category of Ocean jasper, Flint is very common which consists of nodules which comes about when combined with silicic fluid formed around the nucleus circling agglomeration, With sedimentary elements and the pressing of deposits that continuously turns into layers like banded patterns.
The colors are formed due to the presence of oxygen in the sediment, if there is a lot of presence of oxygen, the small of iron is oxidised giving the jasper its yellow or red ocher color. If there is not a lot of oxygen, then the jasper color becomes green or black.
The banded iron formation – also in the category of the Ocean jasper which when formed with large deposits of hematite which alternates with layers of magnetite. The huge concentration of acid in the seawater is known to reflect the silica and the iron content.
For so many millions of years, iron that laid on the seafloor were known to be oxygen that was oxidised, which resulted in the Banded iron formation. Tiger’s eye is also from jasper formation.
Volcanic Jaspers are volcanic rocks that are silicified known as Rhyolites. The chemistry of rocks can be altered by the thermal waters often associated with the flow of silica. Rhyolites were formed due to rock erupting containing more than 70% Silica with varying structures.
Most interesting is that Strati form of rich brown or ochre culminating from the oxidation of the iron is formed, jaspers have a pattern of dune-like layers or lines and are often called ’picture stones ‘or landscape stones.
Massive blocky Jaspers came about due to the change of the rhyolitic tuffs and formed next to the volcanic deposits and are thick. These kind of massive blocky jaspers are quite angular shaped and shows some fractures through which it drains the oxidizing process that carry elements of chromophore. Some of the qualities of massive blocky jaspers are : it shows colors of purple, red, and yellow, high content of opalite, irregular Sharpe mostly angular, showing some fractures. They can also be nodular and sometimes can show dendrites into three dimensions.
Rhyolitic Jaspers – were formed from the lava flows, altering its Rhyolitic state. When lava erupts it cools very fast and it vitrifies, and can transform into a black glass disallowing it to crystallize.
Some features of this Rhyolitic Jasper are: Because they are solid they can only be broken manually, they cannot be classified as nodular.
Jaspers pseudomorphic on fossils. Pseudomorphosis occur when fossils are silicified similar to petrified forest. Fossilisation is a very long process starting from shells, corals, sponges, dinosaur skeletons, algaes,etc.
Chemical Jaspers – were found in nodules or cavities that has no precursors, fossils or volcanic rock, formed by silica colloide and by the intermingling stages of precipitation forming of opal .
Orbed Jaspers – formation are so rare that they are high sought after by collectors and people involved in lapidaries because they are formed like circles and overlaps the main central part of the stone. These Jaspers are so compacted that they are referred to as porcelain and make for a perfect brilliant polish. Shapes can be in the form of geodes, sometimes can be found inside thunder eggs, have a veiny look.
Brecciated Jaspers. Very popular form of Jaspers. They are crafted into inlays into jewellery boxes or inlaid into furniture. These kind of Jaspers have fractures and found in nodules which are quite large. It is a very hard rock and it is impossible to break.
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