Dickite

Dickite
General
CategoryPhyllosilicates
Kaolinite-serpentine group
Formula
(repeating unit)		Al2Si2O5(OH)4
IMA symbolDck[1]
Strunz classification9.ED.05
Dana classification71.01.01.01
Crystal systemMonoclinic
Crystal classDomatic (m)
(same H-M symbol)
Space groupCc
Unit cella = 5.150, b = 8.940
c = 14.424 [Å]; β = 96.8°; Z = 4
Identification
ColorWhite, with coloration from impurities
Crystal habitPseudohexagonal crystals, aggregates of platelets and compact massive
CleavagePerfect on {001}
TenacityFlexible but inelastic
Mohs scale hardness1.5–2
LusterSatiny to pearly
StreakWhite
DiaphaneityTransparent
Specific gravity2.6
Optical propertiesBiaxial (+)
Refractive indexnα = 1.561 – 1.564 nβ = 1.561 – 1.566 nγ = 1.566 – 1.570
Birefringenceδ = 0.005 – 0.006
2V angleMeasured: 50° to 80°
References[2][3][4][5][6][7][8][9][10][11][12]

Dickite (Al2Si2O5(OH)4) is a phyllosilicate clay mineral named after the metallurgical chemist Allan Brugh Dick, who first described it. It is chemically composed of 20.90% aluminium, 21.76% silicon, 1.56% hydrogen and 55.78% oxygen. It has the same composition as kaolinite, nacrite, and halloysite, but with a different crystal structure (polymorph). Dickite sometimes contains impurities such as titanium, iron, magnesium, calcium, sodium and potassium.[3]

Dickite occurs with other clays and requires x-ray diffraction for its positive identification. Dickite is an important alteration indicator[clarification needed] in hydrothermal systems as well as occurring in soils and shales.

Dickite's type location is in Pant-y-Gaseg, Amlwch, Isle of Anglesey, Wales, United Kingdom, where it was first described in 1888.[3] Dickite appears in locations with similar qualities and is found in China, Jamaica, France, Germany, United Kingdom, United States, Italy, Belgium and Canada.[12]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Anthony JW, Bideaux RA, Bladh KW, et al. (1995). "Dickite" (PDF). Handbook of mineralogy. Tucson, Ariz.: Mineral Data Publishing. ISBN 9780962209734. OCLC 20759166.
  3. ^ a b c "Dickite: Mineral information, data and localities". MinDat.org. Retrieved 27 Mar 2019.
  4. ^ "Dickite Mineral Data". webmineral.com. Retrieved 27 Mar 2019.
  5. ^ Cite error: The named reference Dick was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference barth was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference cruz was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference ross was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference hayes was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Brind was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Main was invoked but never defined (see the help page).
  12. ^ a b Brindley GW, Porter AR (1978). "Occurrence of dickite in Jamaica-ordered and disordered varieties". Am. Mineral. 63 (5–6): 554–562. S2CID 41328124.