Mineral Information and Data:

K6(Si10Al6)O32 • 12H2O [CNMNC approved formula]

Named as the potassium-dominant species of the phillipsite series. Species named for William Phillips (1775-1828), English mineralogist and founder of the Geological Society of London. Name approved and defined per nomenclature for zeolite minerals (IMA, 1997).

IMA status : Approved Species 1997 ()
(8th edition) :  (This Dana# Added)
  (77) Tectosilicate Zeolite group
  (77.01) true zeolites
  (77.01.03) Gismondine and related species
(10th edition) :
  (09) Silicates
  (09.G) Tektosilicates with Zeolitic H2O
  (09.GC) Chains of doubly-connected 4-membered rings
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: P21/m
Unit cell: a = 9.865(2)Å, b = 14.300(4)Å, c =8.668(2)Å; β=124:20(3)°, Z = 2
Crystal Habit: Crystals always twinned, pseudosymmetrical; striated || [001] on {010}, to 2 cm. Equant to prismatic, or in spherical radiating aggregates.
Twinning: Cruciform single and double penetration twins on {001}, {021}, {110}, ubiquitous
Color: White
Diaphaneity: Translucent to opaque
Luster: Vitreous
Hardness (Mohs): 4 - 5
Measured Density: 2.2 g/cm3
Cleavage: {010} Distinct, {001} Indistinct
Tenacity: Brittle
Fracture: Uneven
Streak: White
Geologic Setting: Typically in cavities in basalt, of hydrothermal origin; an authigenic mineral in saline lake and hot spring deposits and calcareous deep-sea sediments.
Mineral Association: Zeolites, apophyllite, calcite, nosean, nepheline, olivine, melilite, celadonite


Whitish phillipsite-K crystals scattered on a layer of calcite.
Origin: Iron Monarch open cut, Iron Knob, Middleback Range, Eyre Peninsula, South Australia, Australia.
Field of view: 4.5mm
Photo: © Judy Rowe