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

phosphate mineral Phosphate minerals contain the tetrahedrally coordinated phosphate (PO43−) anion along sometimes with arsenate (AsO43−) and vanadate (VO43−) substitutions, and chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions that also fit i ...

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 ( lkt, link=no, Mni Lúzahaŋ Otȟúŋwahe; "Swift Water City") is the second most populous city in South Dakota and the county seat of Pennington County. Named after Rapid Creek, where the settlement developed, it is in western So ...

. The type locality for Robertsite is the Tip Top mine, Custer County, South Dakota, 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 atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

associated with

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

. 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 vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

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 com ...

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

Chiang Mai Chiang Mai (, from th, เชียงใหม่ , nod, , เจียงใหม่ ), sometimes written as Chiengmai or Chiangmai, is the largest city in northern Thailand, the capital of Chiang Mai province and the second largest city in ...

Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...

in a

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

guano Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...

deposit.Handbook of Mineralogy
/ref> It is associated with

rockbridgeite Rockbridgeite is an anhydrous phosphate mineral in the "Rockbridgeite" supergroup with the chemical formula Fe2+Fe3+4(PO4)3(OH)5. It was discovered at the since-shut-down Midvale Mine in Rockbridge County, Virginia, United States. The research ...

, ferrisicklerite,

leucophosphite Leucophosphite is a phosphatic mineral derived from guano Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, a ...

, jahnsite, montgomeryite, collinsite and

hureaulite Hureaulite is a manganese phosphate with the formula . It was discovered in 1825 and named in 1826 for the type locality, Les Hureaux, Saint-Sylvestre, Haute-Vienne, Limousin, France. It is sometimes written as huréaulite, but the IMA does not r ...

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, bl ...

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 Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

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 minerals ...

s. In the Omo Valley of

Ethiopia Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...

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 preserved ...

fish in

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

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, officially the City of Puerto Princesa (Cuyonon: ''Siyudad i'ang Puerto Princesa''; fil, Lungsod ng Puerto Princesa), is a 1st class highly urbanized city in the Mimaropa region of the Philippines. According to the 2020 census, ...

Palawan Palawan (), officially the Province of Palawan ( cyo, Probinsya i'ang Palawan; tl, Lalawigan ng 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 ...

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

. *Mitridatite group: **

Arseniosiderite Arseniosiderite is a rare arsenate mineral formed by the oxidation of other arsenic-containing minerals, such as scorodite or arsenopyrite Arsenopyrite ( IMA symbol: Apy) is an iron arsenic sulfide (FeAsS). It is a hard ( Mohs 5.5-6) metallic ...

-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