Log In
Englishite
A valid IMA mineral species - grandfathered
This page is currently not sponsored. Click here to sponsor this page.
About Englishite
George L. English
Formula:
K3Na2Ca10Al15(PO4)21(OH)7 · 26H2O
Colour:
Colourless to white, grayish green; colourless in transmitted light.
Lustre:
Vitreous, Pearly
Hardness:
3
Specific Gravity:
2.65 - 2.68
Crystal System:
Monoclinic
Name:
After George Letchworth English (14 June 1864, Philadelphia, Pennsylvania, USA – 2 January 1944, Winter Park, Florida, USA), mineral collector and dealer, New York, New York, USA. A study of his collection of phosphate nodules led to the discovery of several minerals, including this one.
This page provides mineralogical data about Englishite.
Unique Identifiers
Mindat ID:
1383
Long-form identifier:
mindat:1:1:1383:9
IMA Classification of Englishite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
K3Na2Ca10Al15(OH)7(PO4)21·26H2O
First published:
1930
Classification of Englishite
8.DH.55
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
H : With large and medium-sized cations, (OH, etc.):RO4 < 1:1
8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
H : With large and medium-sized cations, (OH, etc.):RO4 < 1:1
42.13.8.1
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
13 : Miscellaneous
42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
13 : Miscellaneous
19.8.21
19 : Phosphates
8 : Phosphates of Al and other metals
19 : Phosphates
8 : Phosphates of Al and other metals
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Egs | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Englishite
Vitreous, Pearly
Transparency:
Transparent
Comment:
Lustre pearly on cleavages.
Colour:
Colourless to white, grayish green; colourless in transmitted light.
Streak:
White
Hardness:
3 on Mohs scale
Tenacity:
Flexible
Cleavage:
Perfect
On {001}, perfect, micaceous.
On {001}, perfect, micaceous.
Density:
2.65 - 2.68 g/cm3 (Measured) 2.69 g/cm3 (Calculated)
Optical Data of Englishite
Type:
Biaxial (-)
RI values:
nα = 1.57 nβ = 1.572 nγ = 1.573
Max. Birefringence:
δ = 0.003
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Moderate (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
No measured or calculated 2V is on file for this mineral, so the value used here (70°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
No measured or calculated 2V is on file for this mineral, so the value used here (70°) is estimated from its recorded refractive indices and optic sign, not from a direct 2V measurement.
Dispersion:
r > v
Optical Extinction:
X = c; Y ≃ a; Z ≃ b.
Comments:
2V small.
Chemistry of Englishite
Mindat Formula:
K3Na2Ca10Al15(PO4)21(OH)7 · 26H2O
Element Weights:
Crystallography of Englishite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Cell Parameters:
a = 38.43 Å, b = 11.86 Å, c = 20.67 Å
β = 111.25°
β = 111.25°
Ratio:
a:b:c = 3.24 : 1 : 1.743
Unit Cell V:
8,780.42 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Layers and aggregates of subparallel plates; friable masses.
Comment:
Class 2/m or m; Space Group A2/a or Aa.
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.94 Å | (100) |
| 17.66 Å | (90) |
| 2.84 Å | (80) |
| 5.57 Å | (60) |
| 2.96 Å | (60) |
| 2.68 Å | (60) |
| 1.71 Å | (50) |
| 3.85 Å | (40) |
| 2.34 Å | (40) |
| 3.08 Å | (30) |
| 2.54 Å | (30) |
| 1.58 Å | (30) |
| 1.36 Å | (30) |
| 1.08 Å | (30) |
| 0.98 Å | (30) |
Comments:
Fairfield, Utah, USA. Data from Moore (1976).
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 21 : Chemically precipitated carbonate, phosphate, iron formations | |
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 34 : Complex granite pegmatites | |
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47c : [Carbonates, phosphates, borates, nitrates] |
Geological Setting:
Complex granitic pegmatite.
Type Occurrence of Englishite
General Appearance of Type Material:
Crusts in variscite nodules.
Place of Conservation of Type Material:
Harvard Unviersity, Cambridge, Massachusetts, USA: #95494.
Associated Minerals at Type Locality:
Other Language Names for Englishite
Common Associates
Associations Based on Photo Data:
| 42 photos of Englishite associated with Montgomeryite | Ca4MgAl4(PO4)6(OH)4 · 12H2O |
| 25 photos of Englishite associated with Roscherite | Ca2Mn2+5Be4(PO4)6(OH)4 · 6H2O |
| 25 photos of Englishite associated with Tiptopite | K2(Na,Ca)2Li3Be6(PO4)6(OH)2 · H2O |
| 13 photos of Englishite associated with Variscite | AlPO4 · 2H2O |
| 11 photos of Englishite associated with Crandallite | CaAl3(PO4)(PO3OH)(OH)6 |
| 10 photos of Englishite associated with Wardite | NaAl3(PO4)2(OH)4 · 2H2O |
Tip Top Mine, Fourmile, Custer Mining District, Custer County, South Dakota, USA