Phosphosiderite

Phosphosiderite is a rare mineral named for its main components, phosphate and iron. The siderite at the end of phosphosiderite comes from "sideros", the Greek word for iron.[3] It was discovered in 1890. It is mined in some parts of Chile, Argentina, Germany, Portugal, and the United States.[4][5] It is totally soluble in Hydrochloric acid and nearly insoluble in nitric acid.[6][5] It is usually cut into a cabochon shape.[7]

Phosphosiderite
Red phosphosiderite between violet strengite. Picture width 4 mm.
General
CategoryPhosphate minerals
Formula
(repeating unit)		Hydrated iron phosphate FePO4•2H2O
IMA symbolPhsd[1]
Crystal systemMonoclinic
Crystal classPrismatic 2/m
Space groupP21/n (no. 14)
Unit cell454.76 ų
Identification
ColorUsually red to pink to purple, sometimes green, usually yellow veined
Crystal habitTabular {010} or stout prismatic [001]
TwinningCommon on {101}, typically as interpenetration
Cleavage{010} Distinct, {001} Indistinct
FractureUneven
Mohs scale hardness3.5–4
LusterVitreous
StreakWhite
DiaphaneityTransparent, translucent
Specific gravity2.74-2.76
Density2.74 - 2.76 measured, 2.76 calculated
Optical propertiesBiaxial (-)
Refractive indexnα = 1.692 nβ = 1.725 nγ = 1.738
Birefringence0.046
PleochroismVisible
2V angleMeasured: 62°, Calculated: 62°
Dispersionr > v, very strong
SolubilityTotally soluble in hydrochloric acid, nearly insoluble in nitric acid
References[2]

Colors

Phosphosiderite is often found in a bright orchid-purple tint with yellow-colored streaks. The vein-like streaks found in the stone are known as cacoxenite. Four other rare color variants are rose red, brown-reddish yellow, mossy green, and dark shades of purple. Phosphosiderite can also be found as a colorless mineral.[8] It is pleochroic; on the X axis around 4° it is light rose, on the Y axis it is carmine red, and on Z it is colorless.[8]

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85: 291–320.
  2. Taxer, K.; Bartl, H. (December 2004). "On the dimorphy between the variscite and clinovariscite group: refined finestructural relationship of strengite and clinostrengite, Fe(PO4). 2H2O". Crystal Research and Technology. 39 (12): 1080–1088. doi:10.1002/crat.200410293.
  3. "siderite". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  4. Minerals, Dakota Matrix. "Phosphosiderite mineral information and data". www.dakotamatrix.com. Retrieved 2021-04-30.
  5. Anthony et al, Handbook of Mineralogy (2001)
  6. "Phosphosiderite". National Gem Lab. 18 March 2017.
  7. "Phosphosiderite gemstone information". www.gemdat.org. Retrieved 2020-09-14.
  8. "Phosphosiderite". www.mindat.org. Retrieved 2021-03-05.
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