Robertsite, Ca₃(Mn³⁺)₄ (PO₄)₂sub>2·3(H₂O) (alternatively formulated Ca₂(Mn₃(PO₄)₃O₂)(H₂O)₃), is a secondary

phosphate mineral Phosphate minerals are minerals that contain the tetrahedrally coordinated phosphate () anion, sometimes with arsenate () and vanadate () substitutions, along with chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions, that also fit in ...

named for Willard Lincoln Roberts (1923–1987), mineralogist and professor at

South Dakota School of Mines The South Dakota School of Mines & Technology (South Dakota Mines, SD Mines, or SDSM&T) is a public university in Rapid City, South Dakota. It is governed by the South Dakota Board of Regents and was founded in 1885. South Dakota Mines offers ba ...

Rapid City, South Dakota Rapid City is the county seat of Pennington County, South Dakota, United States. It is located on the eastern slope of the Black Hills in western South Dakota and was named after Rapid Creek (South Dakota), Rapid Creek, where the settlement deve ...

. The type locality for Robertsite is the Tip Top mine,

Custer County, South Dakota Custer County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 8,318. Its county seat is Custer. The county was created in 1875, and was organized in 1877. It was named after General George Armstr ...

, US. Robertsite occurs at the Tip Top Mine as minute crystal aggregates and crusts found on

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

associated with

triphylite Triphylite is a lithium iron(II) phosphate mineral with the chemical formula LiFePO4.IMA-CNMNC List of Mine ...

. It is a dark reddish brown to black

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

mineral. It occurs as a secondary mineral in

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

. It is also reported from the Khoa Rang Kai phosphate deposit,

Chiang Mai Chiang Mai, sometimes written as Chiengmai or Chiangmai, is the largest city in northern Thailand, the capital of Chiang Mai province and the List of municipalities in Thailand#Largest cities by urban population, second largest city in Thailan ...

Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...

in a

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

guano Guano (Spanish from ) is the accumulated excrement of seabirds or bats. Guano is a highly effective fertiliser due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. Guano was also, to a le ...

deposit.Handbook of Mineralogy
/ref> It is associated with rockbridgeite, ferrisicklerite, leucophosphite, jahnsite, montgomeryite,

collinsite Collinsite is a mineral with chemical formula . It was discovered in British Columbia, Canada, and formally described in 1927. It was named in honor of William Henry Collins (1878–1937), director of the Geological Survey of Canada. There are thr ...

and hureaulite in the type locality. In the guano deposit it occurs with carbonate-

fluorapatite Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blu ...

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 ...

, dolomite,

and

clay mineral Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minera ...

s. In the Omo Valley of

Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...

it occurs with mitridatite associated with

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

fish in

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

sediments. Recently, in an exploration conducted by the Italian La Venta Geographical Association, confirmed the existence of Robertsite in the Puerto Princesa Subterranean River National Park, located about 50 kilometres (31 mi) north of the city center of

Puerto Princesa Puerto Princesa (, American Spanish: , European Spanish: ), officially the City of Puerto Princesa (Cuyonon language, Cuyonon: ''Siyudad i'ang Puerto Princesa''; ), is a Cities of the Philippines#Legal classification, highly urbanized city in th ...

Palawan Palawan (, ), officially the Province of Palawan (; ), is an archipelagic province of the Philippines that is located in the region of Mimaropa. It is the largest province in the country in terms of total area of . The capital and largest c ...

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

. *Mitridatite group: ** Arseniosiderite-mitridatite series: ***Ca₂(Fe³⁺)₃ (AsO₄)₃�3H₂O ***''to'' ***Ca₂(Fe³⁺)₃ (PO₄)₃�3H₂O **Arseniosiderite-robertsite series:Mindat Arseniosiderite-Robertsite Series
/ref> ***Ca₂(Fe³⁺)₃ (AsO₄)₃�3H₂O ***''to'' ***Ca₃(Mn³⁺)₄ (PO₄)₂sub>2·3H₂O

References

* * *Andrade, M. B., Morrison, S. M., Di Domizio, A. J., Feinglos, M. N., & Downs, R. T. (2012). Robertsite, Ca2MnIII3O2 (PO4) 3.3 H2O. Acta Crystallographica Section E: Structure Reports Online, 68(10), i74-i7
doi:10.1107/S160053681203735X
{dead link, date=April 2018 , bot=InternetArchiveBot , fix-attempted=yes Phosphate minerals Manganese(III) minerals Monoclinic minerals Minerals in space group 15