Robertsite, Ca₃₄[(OH)₃| (PO₄)₂]₂·3(H₂O) (alternatively formulated Ca₂(Mn₃(PO₄)₃O₂)(H₂O)₃), is a secondary phosphate mineral named for Willard Lincoln Roberts (1923–1987), mineralogist and professor at South Dakota School of Mines in Rapid City, South Dakota

Rapid City, South Dakota

Rapid City is the second-largest city in the U.S. state of South Dakota, and the county seat of Pennington County. Named after Rapid Creek on which the city is established, it is set against the eastern slope of the Black Hills mountain range. The population was 67,956 as of the 2010 Census. Rapid...

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The type locality for Robertsite is the Tip Top mine, Custer County, South Dakota

Custer County, South Dakota

As of the census of 2000, there were 7,275 people, 2,970 households, and 2,067 families residing in the county. The population density was 5 people per square mile . There were 3,624 housing units at an average density of 2 per square mile...

, USA. Robertsite occurs at the Tip Top Mine as minute crystal aggregates

Aggregate (composite)

Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material. For efficient filling, aggregate should be much smaller than the finished item, but have a wide variety of sizes...

 and crusts found on quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 associated with triphylite. It is a dark reddish brown to black monoclinic mineral.

It occurs as a secondary mineral in pegmatite

Pegmatite

A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

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

Chiang Mai

Chiang Mai sometimes written as "Chiengmai" or "Chiangmai", is the largest and most culturally significant city in northern Thailand. It is the capital of Chiang Mai Province , a former capital of the Kingdom of Lanna and was the tributary Kingdom of Chiang Mai from 1774 until 1939. It is...

, Thailand

Thailand

Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...

 in a limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 guano

Guano

Guano is the excrement of seabirds, cave dwelling bats, and seals. Guano manure is an effective fertilizer due to its high levels of phosphorus and nitrogen and also its lack of odor. It was an important source of nitrates for gunpowder...

 deposit. It is associated with rockbridgeite, ferrisicklerite, leucophosphite, jahnsite, montgomeryite, collinsite and hureaulite

Hureaulite

Hureaulite is a manganese phosphate with the formula Mn2+522·4H2O. It was discovered in 1825 and named in 1826 for the type locality, Les Hureaux, Saint-Sylvestre, Haute-Vienne, Limousin, France...

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

Fluorapatite

Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca53F . Fluorapatite is a hard crystalline solid. Although samples can have various color , the pure mineral is colorless as expected for a material lacking transition metals...

, calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

, dolomite

Dolomite

Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

, quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 and clay minerals. In the Omo Valley of Ethiopia

Ethiopia

Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...

 it occurs with mitridatite associated with fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 fish in Pliocene

Pliocene

The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...

/Pleistocene

Pleistocene

The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

 lake

Lacustrine

Lacustrine means "of a lake" or "relating to a lake".Specifically, it may refer to:*Lacustrine plain*Lacustrine delta-Fish:*Lacustrine goby , a type of small fish found in Philippine waters belonging to the Gobiidae family, known in Tagalog as dulong-See also:*Fluvial - of or relating a...

 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

Puerto Princesa Subterranean River National Park

The Puerto Princesa Subterranean River National Park is located about north of the city centre of Puerto Princesa, Palawan, Philippines. The river also called Puerto Princesa Underground River. The national park is located in the Saint Paul Mountain Range on the northern coast of the island. It is...

, located about 50 kilometres (31 mi) north of the city center of Puerto Princesa, Palawan

Palawan

Palawan is an island province of the Philippines located in the MIMAROPA region or Region 4. Its capital is Puerto Princesa City, and it is the largest province in the country in terms of total area of jurisdiction. The islands of Palawan stretch from Mindoro in the northeast to Borneo in the...

, Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

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• Mitridatite group:
  • Arseniosiderite
    Arseniosiderite
    Arseniosiderite is a rare arsenate mineral formed by the oxidation of other arsenic-containing minerals, such as scorodite or arsenopyrite. It occurs in association with beudantite, carminite, dussertite, pharmacolite, pitticite, adamite and erythrite. The name arseniosiderite reflects two major...
    
    -mitridatite series:
    • Ca₂(Fe³⁺)₃[(O)₂|(AsO₄)₃]·3H₂O
    • to
    • Ca₂(Fe³⁺)₃[(O)₂|(PO₄)₃]·3H₂O
  • Arseniosiderite-robertsite series:
    • Ca₂(Fe³⁺)₃[(O)₂|(AsO₄)₃]·3H₂O
    • to
    • Ca₃(Mn³⁺)₄[(OH)₃|(PO₄)₂]₂·3H₂O