Monohydrocalcite is a mineral that is a hydrous form of calcium carbonate, 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 families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crysta ...

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

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, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including prec ...

lansfordite Lansfordite is a hydrated magnesium carbonate mineral with composition: MgCO3·5H2O. Landsfordite was discovered in 1888 in a coal mine in Lansford, Pennsylvania. It crystallizes in the monoclinic system (space group ''P21/c'') and typically occ ...

, and

nesquehonite Magnesium carbonate, (archaic name magnesia alba), is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals. Forms The most common magnesium carbonate forms are t ...

. Monohydrocalcite has been observed in air conditioning systems, and in

moonmilk Moonmilk (sometimes called mondmilch, also known as montmilch or as cave milk) is a white, creamy substance found inside limestone, dolomite, and possibly other types of caves. It is a precipitate from limestone comprising aggregates of fine cry ...

deposits in caves, both probably formed from spray of carbonate rich fluids. It is well known in

Robe A robe is a loose-fitting outer garment. Unlike garments described as capes or cloaks, robes usually have sleeves. The English word ''robe'' derives from Middle English ''robe'' ("garment"), borrowed from Old French ''robe'' ("booty, spoils" ...

on the

Limestone Coast The Limestone Coast is a name used since the early twenty-first century for a South Australian government region located in the south east of South Australia which immediately adjoins the continental coastline and the Victorian border. The ...

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

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 (also Ysyk-Köl, ky, Ысык-Көл, lit=warm lake, translit=Ysyk-Köl, , zh, 伊塞克湖) is an endorheic lake (i.e., without outflow) in the Northern Tian Shan mountains in Eastern Kyrgyzstan. It is the seventh-deepest lake in th ...

Kyrgyzstan Kyrgyzstan,, pronounced or the Kyrgyz Republic, is a landlocked country in Central Asia. Kyrgyzstan is bordered by Kazakhstan to the north, Uzbekistan to the west, Tajikistan to the south, and the People's Republic of China to the east. ...

Lake Kivu Lake Kivu is one of the African Great Lakes. It lies on the border between the Democratic Republic of the Congo and Rwanda, and is in the Albertine Rift, the western branch of the East African Rift. Lake Kivu empties into the Ruzizi River, which ...

Democratic Republic of the Congo The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...

, and

Solar Lake Solar Lake ( ''Birkat aš-Šams'') is a saline desert lake located on the edge of the Red Sea, about 18 km south of Eilat in the Sinai Peninsula, Taba, Egypt, close to its borders with Israel. A small lake of high salinity, it is the site of ...

Sinai Sinai commonly refers to: * Sinai Peninsula, Egypt * Mount Sinai, a mountain in the Sinai Peninsula, Egypt * Biblical Mount Sinai, the site in the Bible where Moses received the Law of God Sinai may also refer to: * Sinai, South Dakota, a place ...

. It has been reported as a significant component of the decomposition of

ikaite Ikaite is the mineral name for the hexahydrate of calcium carbonate, CaCO3·6H2O. Ikaite tends to form very steep or spiky pyramidal crystals, often radially arranged, of varied sizes from thumbnail size aggregates to gigantic salient spurs. It ...

in the towers of the Ikka Fjord, West

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

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

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

s of the

tiger shark The tiger shark (''Galeocerdo cuvier'') is a species of requiem shark and the last extant member of the family Galeocerdonidae. It is a large macropredator, capable of attaining a length over . Populations are found in many tropical and tempera ...

, the

bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

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'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ani ...

,Catherine, H., Skinner, K., Osbaldiston, G. W., Wilner, A. N. Monohydrocalcite in a guinea pig bladder stone, a novel occurrence.

American Mineralogist ''American Mineralogist: An International Journal of Earth and Planetary Materials'' is a peer-reviewed scientific journal covering the general fields of mineralogy, crystallography, geochemistry, and petrology. It is an official journal of the Min ...

, 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, known as tapeworms. Their bodies consist of man ...

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 a ...

cactus A cactus (, or less commonly, cactus) is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word ''cactus'' derives, through Latin, from the Ancient Greek ...

. 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 and calcite. 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