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Formula: Ca(PO3OH)
Anhydrous acid phosphate
Crystal System: Triclinic
Specific gravity: 2.929 measured, 2.924 calculated
Hardness: 3½
Streak: White
Colour: White, yellow or colourless, colorless in transmitted light
Environments
Monetite occurs as coatings and cements resulting from guano-induced phosphatisation of sedimentary rocks, where it
is associated with newberyite, gypsum,
whitlockite, aphthitalite and
syngenite. Monetite also occurs as a coating on phosphate minerals in
granite
pegmatites, associated with
apatite, lithiophilite,
jahnsite, hureaulite,
barbosalite and whitlockite.
Powdered monetite takes up water from the atmosphere and forms brushite
(Mindat).
Localities
At the Niah Great Cave, Miri Division, Sarawak, Malaysia, monetite occurs in a cave deposit of phosphates
(Dana).
At the Cioclovina cave, Boșorod, Hunedoara, Hunedoara, Romania, the common cave-minerals
calcite, aragonite,
gypsum, hydroxylapatite,
brushite, monetite,
crandallite and taranakite are
accompanied by a number of rare mineral species such as tinsleyite,
sampleite, paratacamite or
clinoatacamite,
churchite-(Y) and foggite
(CM 47.207-208).
At the Măgurici Cave, Sălaj, Romania, the phosphatisation of illite and
montmorillonite clay rich sediments, located on the cave's floor, lead
to the formation of taranakite and
francoanellite. Mineral assemblages precipitated at the boundary between
limestone bedrock and guano deposits are dominantly
hydroxylapatite, brushite,
ardealite and monetite. A number of sulphate minerals such as
gypsum, bassanite,
mirabilite and cesanite were
precipitated along with the phosphates. The major parameters controlling the environments under which these mineral
assemblages were deposited are pH, relative humidity, alkali content and Ca/P ratio
(EJM 15.741-745).
At Ascension Island, Saint Helena, Ascension and Tristan da Cunha, monetite occurs with
apatite and newberyite
(Dana).
At Mona Island, Mayagüez, Puerto Rico, USA, monetite occurs with gypsum
(Dana).
At the type locality, Monito Island, Mayagüez, Puerto Rico, USA, monetite is formed by the interaction of bird
guano in a limestone cave
(Mindat).
At the Los Monges Islands, Federal Dependencies, Venezuela, monetite occurs with
whitlockite
(Dana).
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