Anhydrous phosphate containing hydroxyl, beryllium-bearing mineral
Specific gravity: 2.95
Hardness: 5 to 5½
Colour: Colourless, grey, brown, pale yellow, greenish white, light blue, purple; colourless in transmitted light. May be blue-green or blue in daylight, lavender or light violet in incandescent light (Mindat).
Solubility: Soluble in acids
Hydroxylherderite is found usually as a pegmatite mineral formed during late stage hydrothermal deposition in crystal-lined
(Mindat, Webmin, HOM).
It may form from the alteration of beryl or
(HOM, AM 63.913).
Associated minerals include elbaite, topaz,
fluorite and quartz
(HOM, R&M 87.5.449).
The presence of these species can indicate very high fluorine activity at the time of formation. Hydroxylherderite forms late,
when most of
the fluorine may have been consumed by the other fluorine-bearing mineral species, and only in rare cases will sufficient fluorine
be left over to form herderite
At Minas Gerais, Brazil, hydroxylherderite is associated with lepidolite, elbaite, topaz and microlite (Dana).
At the Sapo mine, Minas Gerais, Brazil, hydroxylherderite is a rare accessory mineral in the pegmatite, normally found inside tourmaline-bearing cavities (Min Rec 40.4.290).
In the Erongo Mountains, Namibia, hydroxylherderite is found in crystal-lined cavities associated with schorl, muscovite and orthoclase (MinRec 37.5.419).
At Klein Spitzkoppe, Namibia, hydroxylherderite has been found associated with euclase (MinRec 36.4.325).
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, hydroxylherderite is common, and commonly associated with fluorapatite and earlier pegmatite minerals including muscovite, quartz and feldspars. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.509).
At the Crooker Gem Pegmatite, Newry, Oxford county, Maine, USA, the mitridatite-coated fractures are rich in phosphate species. The mitridatite is the first phosphate to develop in the fracture, followed by jahnsite, laueite, phosphosiderite, pseudolaueite, rockbridgeite, stewartite, strunzite, whitmoreite, and xanthoxenite, all of which have overlapping formation. Fluorapatite, eosphorite, hydroxylapatite, hydroxylherderite and zanazziite are found in the Crooker gem pegmatite but are not found in late fractures (R&M 87.5.446).
At the Newry mine, Oxford county, Maine, USA, hydroxylherderite is an alteration product of beryllonite (Dana, Mindat).
The Fletcher mine, Groton, Grafton County, New Hampshire, USA, is the premier New Hampshire locality for hydroxylherderite. Crystals found here are not in the phosphate pods derived from the alteration of triphylite but in pockets that are some distance away from them. The pockets are 10 to 15 cm in diameter and contain millimeter-sized muscovite crystals and hydroxylherderite crystals to 5 cm, ranging in colour from dark brown to a light greenish brown to yellowish brown or cream-coloured (R&M 97.3.224-226).
At the Palermo No. 1 mine, Groton, Grafton County, New Hampshire, USA, hydroxylherderite occurs as thick tabular to pseudohexagonal crystals as well as radiating fibrous aggregates. They can range from colourless, pale green, yellow-green and tan, to reddish-brown (R&M 97.3.224-226).
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