Calcite is a calcium carbonate filter medium that corrects the pH to achieve a non-corrosive equilibrium.
Calcite is a common mineral of the calcite group, belonging to the calcite-rhodochrosite series. It is a carbonate with the molecular formula CaCo3. It belongs to the triangular system, in nature we can find it from amorphous to an infinity of different crystals, being the most common or outstanding the scaly, pointed or dogtooth, hexagonal, rhombic… Like quartz, we can find it all over the planet.
Pure calcite is colorless or white, but because it contains various impurities it can be almost any color: red, pink, yellow, green, green, blue, lavender, black or brown. It can be transparent, translucent or opaque.
Its luminosity varies from vitreous to opaque, many crystals, especially colorless ones, have a vitreous color, while granular substances, especially fine grains, tend to be opaque. Calcite ranks third on the Mohs hardness scale, it can be easily scratched with a razor or a geological pick.
Its specific gravity is 2.71. Three perfect divisions give calcite a hexagonal polyhedron with rhombic faces, the angles defining the faces being 78 and 102 degrees.
One of the advantages of Calcite is its self-limiting property. When properly applied, it corrects the pH sufficiently to achieve a non-corrosive equilibrium.
Under normal conditions, upon contact with the Calcite, the acidic waters slowly dissolve the calcium carbonate to raise the pH, which reduces the potential leaching of copper, lead and other metals found in typical pumping systems.
Refilling and backwashing
Depending on pH, water chemistry and service flow, the Calcite bed should be periodically refilled when the Calcite is depleted. Because calcium carbonate neutralizes the water, it will increase the hardness and it will then be necessary to use a softener after the neutralizing filter. Upon contact with the calcite, the acidic waters slowly dissolve the calcium carbonate to raise the pH, which reduces the potential leaching of copper, lead and other metals found in typical plumbing systems. Periodic backwashing will prevent excessive fouling, reclassify the bed and maintain high service capacities.
Uses of calcite
Granular calcite (either marble or north-south limestone) can be used both as a sediment, turbidity and ferric iron filter and as a calcium carbonate bed for pH correction. In general, a calcite filter will remove approximately one-third of the total ferric and ferrous iron content of a water supply.
The solubility rate of calcite is dependent on several factors. In relatively free mineral water, the average rate is 0.001 percent (about one-tenth of an ounce of calcite per gallon of water) at 77°F (25°C), but solubility increases in the presence of CO2.
Solubility is also increased by falling temperatures and increasing total pressure.
At the same time, an advantage of calcite is that it does not “over-correct” the pH; thus it will raise the pH uniformly under proper operating conditions.
Backwash flow is very important because of the high mineral density and should be done at a minimum of 8 gpm per square foot of bed area for good performance. If iron is present, a minimum of 10 gpm should be used. Backwashing should be carried out for no less than 10 minutes to remove dirt, iron and calcite precipitates. The most common cause of pH neutralizer failure is the lack of periodic backwashes.
Other applications of calcite
Calcite is the main calcium mineral, fundamental in construction and the basis of cement. It is also important in the production of fertilizers, metals, glass, rubber and paints. The distinctive Icelandic spar, in which the birefringence is very pronounced, is used as a prism in polarizing microscopes and other optical devices.
This mineral also forms rocks that are used for decorative purposes, such as marble, striped granite and tuff. It is also the main ingredient of chalk that can be converted into chalk. For collectors, it is one of the best known and most frequently collected minerals. Most specimens are inexpensive, with the exception of those with a special crystal shape and size, or the classics.
- In animal feed
- Antacids – calcium carbonate
- Paper manufacturing
- Optical applications
- waste treatment
Where is calcite found?
There are thousands of good places to find this mineral, and such a guide could not list them all. Only a few are mentioned here. The original varieties of Icelandic spar were described in an old mine called Helgustadir Mine on the east coast of Iceland at Reydarfjörder, dating back to 1600.
The two classic European regions where this mineral is found are St. Andreasberg in the Harz Mountains in Germany and Pribram in the Czech Republic. Collectors from Birigg and Egremont, Cumbria, England, know prismatic crystals of colorless calcite. Yellow and orange calcite crystals, sometimes distinctive “twinned butterflies”, from Malmberget, Lapland, Sweden. Most of the Icelandic hybrids on the market today originate in Chihuahua, Mexico.