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Cairncrossite

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Professor Bruce Cairncross
Formula:
Sr2Ca7–xNa2x(Si4O10)4(OH)2(H2O)15–x (with 0 ≤ x ≤ 1)
simplified formula of Na-rich crystals: SrCa3Na(Si4O10)2(OH)(H2O)7 (Z = 2).
Colour:
Colourless
Lustre:
Vitreous, Pearly
Hardness:
3
Specific Gravity:
2.846 (Calculated)
Crystal System:
Triclinic
Member of:
Name:
Named after Professor Bruce Cairncross (born 13 August 1953), Head of the Department of Geology 2003-2015 at the University of Johannesburg, Johannesburg, South Africa, in recognition of his work on the mineralogy of South Africa and especially its Mn deposits.


Belongs to both the Gyrolite and Reyerite groups. The combination of elements in the mineral is unique.

The structure is based on sheets of edge-sharing CaO6 octahedra. The sheets link by corners, on both sides, to silicate layers. Layers of paired edge-sharing SrO8 polyhedra are intercalated between the former units. The Sr polyhedra are further bound to disordered NaO6 polyhedra. Linkage to adjacent silicate layers is strenghtened by a complex system of hydrogen bonds.


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Classification of CairncrossiteHide

Approved
Approval Year:
2013

Physical Properties of CairncrossiteHide

Vitreous, Pearly
Transparency:
Transparent, Translucent
Colour:
Colourless
Comment:
Appears white
Streak:
White
Hardness:
Tenacity:
Sectile
Cleavage:
Perfect
|| (001)
Comment:
"sectile before brittle fracture"
Density:
2.846 g/cm3 (Calculated)

Optical Data of CairncrossiteHide

Type:
Biaxial (+)
RI values:
nα = 1.518(2) nβ = 1.522(2) nγ = 1.546(2)
2V:
Measured: 33.9° (6), Calculated: 44.97°
Max Birefringence:
δ = 0.028
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
Low
Dispersion:
weak (r < v)
Pleochroism:
Non-pleochroic
Comments:
indicatrix orientation: Z ∧ c* = 10°

Chemical Properties of CairncrossiteHide

Formula:
Sr2Ca7–xNa2x(Si4O10)4(OH)2(H2O)15–x (with 0 ≤ x ≤ 1)

simplified formula of Na-rich crystals: SrCa3Na(Si4O10)2(OH)(H2O)7 (Z = 2).
IMA Formula:
Sr2Ca7-xNa2x(Si4O10)4(OH)2(H2O)15-x, (0≤x≤1)
Common Impurities:
Na

Crystallography of CairncrossiteHide

Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 9.6265(5) Å, b = 9.6391(5) Å, c = 15.6534(10) Å
α = 100.89(1)°, β = 91.27(1)°, γ = 119.73(1)°
Ratio:
a:b:c = 0.999 : 1 : 1.624
Unit Cell V:
1227.08 ų
Z:
1

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
15.27 (or 15.23)
5.091 (or 5.080)
4.198 (11)
4.136 (8)
3.818 (or 3.807)
3.164 (10)
3.071 (10)
3.061 (or 3.045)

Type Occurrence of CairncrossiteHide

General Appearance of Type Material:
radiating platy-micaceous aggregates, up to 1 cm
Place of Conservation of Type Material:
In the collections of the Institute of Mineralogy and Crystallography, University of Vienna, Vienna, Austria, registration number 13079
Geological Setting of Type Material:
dump material (within Mn ore)
Associated Minerals at Type Locality:

Synonyms of CairncrossiteHide

Other Language Names for CairncrossiteHide

Relationship of Cairncrossite to other SpeciesHide

Member of:
Other Members of this group:
GyroliteNaCa16Si23AlO60(OH)8 · 14H2OTric.
OrlymaniteCa4Mn3Si8O20(OH)6 · 2H2OHex.
TungusiteCa4Fe2Si6O15(OH)6

Common AssociatesHide

Associated Minerals Based on Photo Data:
Richterite1 photo of Cairncrossite associated with Richterite on mindat.org.
Sugilite1 photo of Cairncrossite associated with Sugilite on mindat.org.
Pectolite1 photo of Cairncrossite associated with Pectolite on mindat.org.

Fluorescence of CairncrossiteHide

light-blue, intense (SWUV)

Other InformationHide

Thermal Behaviour:
25–400oC: two-phase endothermic weight loss of water vs nearly complete rehydration capability up to 400oC
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for CairncrossiteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Giester, G., Lengauer, C.L., Pristacz, H., Rieck, B. and von Bezing, K.-L. (2013) Cairncrossite, IMA 2013-012. CNMNC Newsletter No. 16, August 2013, page 2703; Mineralogical Magazine, 77, 2695-2709.
Pristacz, H., Giester, G., Rieck, B., Lengauer, C.L. (2013): Thermal behaviour of the new mineral Cairncrossite, Sr2Ca7(Si4O10)4(OH)2·15H2O. Poster, MinPet 2013, September 19-23; abstract in Mitt. Österr. Mineral. Ges. 159 (in press) [http://erdwissenschaften.uni-graz.at/aktuelles/veranstaltungen/minpet2013/downloads/ThirdCircular2013_Final.pdf]
Giester, G., Lengauer, C.L., Pristacz, H., Rieck, B., Topa, D., Von Bezing, K.L.(2016): Cairncrossite, a new Ca-Sr (-Na) phyllosilicate from the Wessels Mine, Kalahari Manganese Field, South Africa. European Journal of Mineralogy 28, 495-505.

Internet Links for CairncrossiteHide

Localities for CairncrossiteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
South Africa (TL)
 
  • Northern Cape Province
    • Kalahari manganese field
      • Hotazel
Giester, G., Lengauer, C.L., Pristacz, H., Rieck, B. and von Bezing, K.-L. (2013) Cairncrossite, IMA 2013-012. CNMNC Newsletter No. 16, August 2013, page 2703; Mineralogical Magazine, 77, 2695-2709.; Giester, G., Lengauer, C.L., Pristacz, H., Rieck, B., Topa, D., von Bezing, K.-L. (2016): Cairncrossite, a new phyllosilicate from the Wessels Mine, Kalahari Manganese Field, South Africa. European Journal of Mineralogy, 28, 495-505
Mineral and/or Locality  
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