Steacyite - Occurrence, Properties, and Distribution

May 10 2013

Topics Covered

Introduction to Steacyite
Properties of Steacyite
How to Identify Steacyite
Global Distribution
Occurrence of Steacyite and Useful Mineral Association
References

Introduction to Steacyite

Chemical Formula – K_1-x(Ca,Na)₂ThSi₈O₂₀,

where x=0.2 to 0.4

Steacyite is a complex silicate mineral first discovered at Mont-Saint-Hilaire, Quebec, in 1982. The mineral was named after Harold Robert Steacy, mineralogist, former Curator of the National Mineral Collection, Geological Survey of Canada.

Properties of Steacyite

The following are the key properties of steacyite:

Cell Data
- Space Group: P4=mcc
- a = 7.58(1)
- c = 14.77(2)
- Z = 2
Crystal Data
- Tetragonal
- Point Group: 4=m 2=m 2=m
- As crystals elongated || [001], terminated by {100} and {001}, to 2 mm; radiating crystalline; massive
- Twinning: Cruciform, by 90° rotation about [010]
- X-ray Powder Pattern: 3.38 (100), 3.32 (55), 5.30 (45), 2.64 (41), 2.00 (26), 1.82 (20), 2.16 (19)

Chemical Composition

Elements	Content 1	Content 2
SiO₂	57.92	52.12
ThO₂	28.03	30.08
CaO	4.92	4.38
K₂O	3.42	4.42
Na₂O	3.36	3.96
MnO	1.64	-
RE₂O₃	0.47	1.81
MgO	0.17	-
As₂O₃	-	0.45
UO₂	-	0.14
PbO	0.07	-
F	-	0.23

Optical Properties
- Optical Class: Uniaxial (-)
- ω = 1.573(1)
- ε = 1.572(1)

Estimated Properties

Electron density	Bulk density (electron density)=2.77 g/cm³ note: Specific gravity of Steacyite =2.95 g/cm³
Photoelectric	PE_Steacyite = 568.46 barns/electron U= PE_Steacyite x ρElectron density= 1575.62 barns/cm³
Fermion index	Fermion index = 0.01 Boson index = 0.99
Radioactivity	Steacyite is radioactive

How to Identify Steacyite

Steacyite is brown or yellow green in color. It is radioactive, and has translucent appearance, white streak and vitreous color. Its fractures are brittle as shown by most of the non-metallic minerals and glasses. It can be formed as massive radial crystals that radiate from a center without producing stellar forms. The density of steacyite is 2.95 g/cm³, and its relative hardness is 5.

Global Distribution

Steacyite is distributed in the following places:

Mont Saint-Hilaire, Quebec, Canada
Rouma Isle, Los Islands, Guinea
Dara-i-Pioz massif, Alai Range, Tien Shan, Tajikistan

Occurrence of Steacyite and Useful Mineral Association

Steacyite occurs in a miarolitic cavity in nepheline syenite, cavities in pegmatite veins in nepheline syenite in an intrusive alkalic gabbro-syenite complex, albitites in syenites and quartz-albite-aegirine veinlets. It is closely associated with titanite, miserite, baratovite, villiaumite, serandite, eudialyte, catapleiite, astrophyllite, arfvedsonite, aegirine, analcime and nenadkevichite.