Monohydrocalcite is a mineral that is a hydrous form of

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

, CaCO₃·H₂O. It was formerly also known by the name hydrocalcite, which is now discredited by the IMA. It is a

trigonal In crystallography, the hexagonal crystal family is one of the six crystal family, crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the tr ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

which is white when pure. Monohydrocalcite is not a common rock-forming mineral, but is frequently associated with other calcium and magnesium

carbonate minerals Carbonate minerals are those minerals containing the carbonate ion, . Carbonate divisions Anhydrous carbonates *Calcite group: trigonal **Calcite CaCO3 **Gaspéite (Ni,Mg,Fe2+)CO3 **Magnesite MgCO3 **Otavite CdCO3 **Rhodochrosite MnCO3 **Sider ...

, such as

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...

, lansfordite, and nesquehonite. Monohydrocalcite has been observed in air conditioning systems, and in moonmilk deposits in caves, both probably formed from spray of carbonate rich fluids. It is well known in Robe on the Limestone Coast of

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

as a component of beach sands of Lake Fellmongery and Lake Butler, where it is believed to be formed from algal spume. Other lacustrine deposits include Lake

Issyk-Kul Issyk-Kul () or Ysyk-Köl (, ; ) is an endorheic saline lake in the western Tianshan Mountains in eastern Kyrgyzstan, just south of a dividing range separating Kyrgyzstan from Kazakhstan. It is the eighth-deepest lake in the world, the eleve ...

Kyrgyzstan Kyrgyzstan, officially the Kyrgyz Republic, is a landlocked country in Central Asia lying in the Tian Shan and Pamir Mountains, Pamir mountain ranges. Bishkek is the Capital city, capital and List of cities in Kyrgyzstan, largest city. Kyrgyz ...

, Lake Kivu,

Democratic Republic of the Congo The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...

, and Solar Lake, Sinai. It has been reported as a significant component of the decomposition of ikaite in the towers of the Ikka Fjord, West

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

. It is also noted for its bizarre occurrences, which include inside the

otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...

s of the tiger shark, the bladder of a

guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy ( ), is a species of rodent belonging to the genus ''Cavia'', family Caviidae. Animal fancy, Breeders tend to use the name "cavy" for the ani ...

,Catherine, H., Skinner, K., Osbaldiston, G. W., Wilner, A. N. Monohydrocalcite in a guinea pig bladder stone, a novel occurrence. American Mineralogist, 62: 273 – 277, 1977. the calcareous corpuscles of a

cestode Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, commonly known as tapeworms. Their bodies co ...

parasite, and the final stages of decomposition of the putrefying flesh of the giant

saguaro The saguaro ( , ; ''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...

cactus. These occurrences suggest a biochemical origin is possible.

Formation of monohydrocalcite

Monohydrocalcite forms via a Mg-rich amorphous calcium carbonate (ACC) precursor. This Mg-rich ACC forms rapidly (seconds) and then transforms to monohydrocalcite via dissolution and reprecipitation, with monohydrocalcite forming via a nucleation-controlled reaction like spherulitic growth. Recent studies have highlighted the importance of Mg in the formation process of monohydrocalcite. The presence of Mg in solution is known to inhibit the formation of

vaterite Vaterite is a mineral, a polymorphism (materials science), polymorph of calcium carbonate (calcium, Cacarbon, Coxygen, O3). It was named after the German mineralogist Heinrich Vater. It is also known as mu-calcium carbonate (μ-CaCO3). Vaterite b ...

and

. However, the hydrated nature of monohydrocalcite means that full dehydration of Mg is not required before incorporation of this ion into this mineral and therefore it will more likely form than the anhydrous calcium carbonate phases.

Footnotes

External links

Webmineral
Calcium minerals Carbonate minerals

Formation of monohydrocalcite

Footnotes

Further reading

External links