Frondelite

minerals

rockbridgeite

vivianite

heteroseite

Formula:Mn2+Fe3+4(PO4)3(OH)5
Anhydrous phosphate containing hydroxyl, rockbridgeite group and forms a series with rockbridgeite
Specific gravity: 3.543
Hardness: 4½
Streak: Green (unoxidized), brown (oxidized)
Colour: Dark brown, ochre-yellow, red-brown, greenish black, greenish brown, black; rarely orange
Solubility: Frondelite is easily fusible to a magnetic globule. It is soluble in dilute hydrochloric acid, but insoluble in nitric and sulphuric acids; the Na2CO3 fusion is insoluble in nitric acid but soluble in HCI; the KHSO4 fusion is soluble in sulphuric acid (AM 34.541-549).
Environments

Pegmatites

Frondelite is a secondary mineral resulting from the alteration of primary phosphates in complex granite pegmatites (Mindat, HOM).

At the type locality, the Sapucaia mine, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil, frondelite was found in a granite pegmatite associated with vivianite, triphylite, heterosite, purpurite, phosphosiderite, leucophosphite and cyrilovite (Mindat, HOM).

At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, frondelite occurs as crystals to 2 mm. Some rockbridgeite shows a change to frondelite along the length of the crystals. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.508).

At the Fletcher mine, North Groton, New Hampshire, USA, frondelite has been found with phosphosiderite (Dana).

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