How is pyrite processed

It is interesting to start a collection illustrating the various crystal forms. Pyrite forms in almost all types of environments including sedimentary, igneous, and metamorphic, as well as hydrothermal veins.

Richard P. Pyrite is a common accessory mineral in sedimentary rocks, particularly in limestone, sandstone and carbonaceous siltstones or shales. Some times we wonder who and why it got there; and what does it mean for petroleum exploration. Originally the iron came from the weathering of older igneous or metamorphic rocks.

Iron is a common minor constituent of all continental igneous rocks; and occurs in minerals such as ilmenite, magnetite and pyrite, and ferro-magnesian silicates like olivine, pyroxene, amphibole, and biotite mica.

Deep weather over long periods of geologic time releases the iron and soluble iron salts form. The dissolved iron then travels in solution to the sea, where ferrous iron is oxidised and deposited. Much of the pyrite contained in sediments and sedimentary rocks is authigenic, formed in the depositional environment, or early diagenetic, formed during the transformation of the sediment into rock lithification.

The formation of pyrite requires the presence of organic matter in the sediment, sulphate in solution in the pore water, and locally anerobic reducing chemical environment. It is the presence of decaying organic matter in the sediment that creates the reducing chemical environment. In marine environments, decay of organic matter occurs most rapidly just below the bottom of the sea, before more than a few centimetres of other sediment have accumulated on top of it.

With deeper burial, most of the reactive organic matter has already been consumed and no more pyrite can form. Pyrite seldom forms in fresh-water environments. The formation of pyrite crystals depends mainly on the iron content of the sediment. The process of pyrite formation in sediments results from the action of bacteria, which reduce sulphate ions dissolved in the pore water to sulphide.

If there is iron present, iron sulphide crystals begin to grow. These sulphate —reducing bacteria also need other nutrients to live, which are provided by organic carbon in the sediment. Pyrite can also precipitate in reducing sulphate — rich environments created by the migration of crude oil into the rock system in deeper layers. This pyrite generally forms larger crystals, which tend to fill pre-existing pore spaces in the rock and overlay any primary cement present. The significance of pyrite for oil-finders is that its presence proves the chemically reducing conditions rather than oxidising conditions prevailed at some time in the past.

Reducing conditions allow organic carbon to be preserved, whether in the form of plant or animal remains, coaly sediments or petroleum. The pyrite —sulphur content of the sediment correlates directly with the total organic carbon content of the rock, which is a measure of petroleum source rock richness.

During colonial times, some intrepid British explorers wanted to establish a new colony on the coast of Labrador, but were denied the funding because they had not found any gold there.

Not to be deterred, they collected some fine specimens of pyrite and sent them back as proof of a gold discovery, and the ruse worked! The Queen looked at the samples but not too closely and immediately approved the building of the colony.

It was a hundred years before the trick was discovered. It is fairly easy to differentiate between gold and pyrite. Although their colours are similar, pyrite tends to be slightly lighter and more brassy in colour. If in doubt, just compare the colour of the sample with some good quality gold jewellery. Gold is much softer than pyrite, so soft that you can scratch it with your fingernail while it takes a good sharp knife blade to scratch pyrite.

The crystal form of pyrite is another dead give-away, with perfect cubic crystals fairly common. Gold can form crystals, but they are extremely rare. As a final check, rub the sample on a rough, unglazed pottery surface, pyrite leaves a distinctive black streak, while gold leaves a golden streak. Chalcopyrite occurs at numerous localities worldwide. It is the most abundant copper-bearing mineral. Chalcopyrite is a primary mineral in hydrothermal veins, disseminations and massive replacements.

Chalcopyrite and dolomite on dolostone. Unknown Locality. Notice the iridescent colouring on the surface of the chalcopyrite. If you were to rub the mineral vigorously with a hard object then if pyrite it will give off a sulphurous smell like rotten eggs but if gold no odour will be apparent. Iron is typically recovered from iron oxides, which occur in larger deposits than pyrite and are more easily mined and refined. There are more economical sources of sulfur nowadays than pyrite - for example, as a byproduct of natural gas and petroleum refining.

What pyrite is mined now is because pyrite is often associated with gold, and may even contain some gold as an impurity. Many mineral collectors like specimens of pyrite, because many tend to be showy and large and are easily accessible, but pyrite turns out to be a nuisance in many ways. Pyrite is common in coal deposits, but burning coal that contains pyrite releases sulfur, which combines with oxygen to form sulfur dioxide, an air pollutant.

The mineral always has a brass-yellow color, a metallic luster and a high specific gravity. It is harder than other yellow metallic minerals, and its streak is black, usually with a tinge of green. It often occurs in well-formed crystals in the shape of cubes, octahedrons, or pyritohedrons, which often have striated faces.

The only common mineral that has properties similar to pyrite is marcasite , a dimorph of pyrite with the same chemical composition but an orthorhombic crystal structure. Marcasite does not have the same brassy yellow color of pyrite.

Instead it is a pale brass color, sometimes with a slight tint of green. Marcasite is more brittle than pyrite and also has a slightly lower specific gravity at 4. Specimen is approximately 3 inches 7. Pyrite and gold can easily be distinguished. Gold is very soft and will bend or dent with pin pressure.

Pyrite is brittle, and thin pieces will break with pin pressure. Gold leaves a yellow streak, while pyrite's streak is greenish black. Gold also has a much higher specific gravity. A little careful testing will help you avoid the " Fool's Gold " problem. Massive Pyrite: Massive pyrite from Rico, Colorado. The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties.

Inexpensive mineral collections are available in the Geology. Pyrite is composed of iron and sulfur; however, the mineral does not serve as an important source of either of these elements. Iron is typically obtained from oxide ores such as hematite and magnetite. These ores occur in much larger accumulations, the iron is easier to extract and the metal is not contaminated with sulfur , which reduces its strength.

Pyrite used to be an important ore for the production of sulfur and sulfuric acid. Today most sulfur is obtained as a byproduct of oil and gas processing. Some sulfur continues to be produced from pyrite as a byproduct of gold production. Pyrite is occasionally used as a gemstone. It is fashioned into beads, cut into cabochons , faceted, and carved into shapes.

This type of jewelry was popular in the United States and Europe in the mid- to lates. Most of the jewelry stones were called "marcasite," but they are actually pyrite. Marcasite would be a poor choice for jewelry because it quickly oxidizes, and the oxidation products cause damage to anything that they contact.

Pyrite is not an excellent jewelry stone because it easily tarnishes. The most important use of pyrite is as an ore of gold. Gold and pyrite form under similar conditions and occur together in the same rocks.

In some deposits small amounts of gold occur as inclusions and substitutions within pyrite.