Mineral Information and Data:

Ca5(PO4)3OH [CNMNC approved formula]

Named in 1856, renamed Apatite-(CaOH) in 2008, and reversed renamed in 2010 as the hydroxyl end-member and from the Greek apatao - "I am misleading.".

IMA status : Renamed IMA Approved; 2010 ()
(8th edition) :  
  (41) Anhydrous Phosphates Containing Hydroxyl or Halogen
  (41.08) where (A)5 (XO4)3 Zq
  (41.08.01) Apatite Group
(10th edition) :
  (08) Phosphates, Arsenates, Vanadates
  (08.B) Phosphates, etc. with Additional Anions, without H2O
  (08.BN) With only large cations, (OH, etc.):RO4 = 0.33:1
Crystal system: Hexagonal System
Point group (H-M): 6/m — dipyramidal
Unit cell: a = 9.41Å, c = 6.88Å
Crystal Habit: As tabular to prismatic crystals, to 30 cm; usually as stalagmites, nodules, in crystalline to massive crusts.
Color: White, wax-yellow, sea-green, brown, black
Diaphaneity: Transparent to translucent
Luster: Vitreous to subresinous, earthy
Hardness (Mohs): 5
Measured Density: 3.14 – 3.21 g/cm3
Cleavage: 2; poor on {0001} and {1010}
Tenacity: Brittle
Fracture: Conchoidal
Geologic Setting: Much less common than fluorapatite. Formed by the reaction of limestone with phosphatic solutions derived from guano. In talc schists associated with serpentinite. As a fracture-localized alteration of montebrasite in a complex granite pegmatite.
Mineral Association: Brushite, calcite (caves); talc, serpentine (schists); montebrasite, crandallite, muscovite (pegmatite)
Synonyms/varieties: Apatite-(CaOH)
Other Properties: BioMineral.
Comments: Hydroxylapatite - Renamed to Apatite-(CaOH) by Mineralogical Record, v39 (2008), p 131. However, it was reversed back to Hydroxylapatite in 2010. In addition, apatite-CaOH)-M is renamed to hydroxylapatite-M and is defined as a monoclinic variant of hydroxylapatite and is not considered a distinct species:
Pasero M, Kampf A R, Ferraris C, Pekov I V, Rakovan J R, White T J (2010) Nomenclature of the apatite supergroup minerals, European Journal of Mineralogy 22, 163-179


Tabular hydroxylapatite crystals on cream colored feldspar
Origin: Sapo Mine, Minas Gerais, Brazil
Sample size: 3.4 x 2.5 x 1.4 cm
Photo: John Veevaert, Trinity Mineral Co


(zoom-in of above)