Steacyite
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Steacyite was named in 1982 by Guy Perrault and Jan T. Szymaňski in honor of Harold Robert Steacy (June 7, 1923 - April 7, 2012), mineralogist, former Curator of the National Mineral Collection, Geological Survey of Canada, for his contributions to Canadian mineralogy.

Discovered in 1981; IMA status: Valid (IMA approved 1981)

Chemistry

Chemical Formula:

K_1-x(Na;Ca)₂ThSi₈O₂₀  (x = 0.2 to 0.4)

Potassium Sodium Calcium Thorium Manganese Silicate

Molecular Weight:

825.70 gm

Composition:

Potassium

2.84 %

K

3.42 %

K₂O

Sodium

1.95 %

Na

2.63 %

Na₂O

Calcium

3.40 %

Ca

4.75 %

CaO

Thorium

25.29 %

Th

28.78 %

ThO₂

Manganese

1.33 %

Mn

1.72 %

MnO

Silicon

27.21 %

Si

58.21 %

SiO₂

Oxygen

37.98 %

O

100.00 %

99.52 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/E.10-30

Nickel-Strunz 10th Ed. ID:

9.CH.10

9 : SILICATES (Germanates)
C : Cyclosilicates
H : [Si₄O₁₂]₈- 4-membered double rings

Related to:

Steacyite Group.

Members of Group:

Steacyite Group: Arapovite, Iraqite-(La), Steacyite, Turkestanite

Varieties:

None

Synonyms:

Desourdyite, IMA1981-E, Unnamed (MSH UK-4)

Crystal Data

Crystallography:

Tetragonal - Ditetragonal Dipyramidal

Crystal Habit:

As crystals elongated || [001], terminated by {100} and {001}, to 2 mm; radiating, crystalline, massive.

Twinning:

Cruciform, by 90° rotation about [010].

Physical Properties

Cleavage:

None

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

5.0

Density:

2.95 (g/cm³)

Luminescence:

Radioactive; emitting alpha (α) and beta (ß) particles, but not gamma (γ) radiation.

Radioactivity:

Strong; GRapi = 506,988.54 (PPB) (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Dark brown, beige, green, yellow.

Transparency:

Translucent, Opaque; Translucent to Transparent in thin section

Luster:

Vitreous, Greasy, Dull

Refractive Index:

1.572 - 1.573  Uniiaxial ( - ) 

Birefringence:

0.0010

Dispersion:

n/a

Pleochroism:

None

Occurances

Geological Setting:

In cavities in pegmatite veins in nepheline syenite in an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada); in a miarolitic cavity in nepheline syenite (Rouma Isle, Guinea); in quartz-albite-aegirine veinlets and in albitites in syenites (Dara-i-Pioz massif, Tajikistan).

Common Associations:

Nenadkevichite, Analcime, Aegirine (Mont Saint-Hilaire, Canada); Arfvedsonite, Astrophyllite, Catapleiite, Eudialyte, Serandite, Villiaumite (Rouma Isle, Guinea); Aegerine, Charoite, Baratovite, Microcline, Miserite, Titanite, Tinaksite (Sirenevyi Kamen' Deposit, Murunskii Massif, Chara and Tokko Rivers Confluence, Aldan Shield, Sakha Republic (Saha Republic; Yakutia), Eastern-Siberian Region, Russia).

Common Impurities:

As, Mn, Pb, F, P

Type Locality:

Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry; Carrière Mont Saint-Hilaire), Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada

Year Discovered:

1981

View mineral photos:

Steacyite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Steacyite is a complex silicate mineral containing Thorium (Th). The Thorium causes Steacyite to be stongly radioactive and emitting alpha (α) and beta (ß) particles, but not gamma (γ) radiation. Steacyite was discovered in 1981 at the Poudrette Quarry, Mount Saint-Hilaire, Québec, Canada and named in 1982 by Guy Perrault and Jan T. Szymaňski in honor of Harold Robert Steacy (June 7, 1923 - April 7, 2012), mineralogist, former Curator of the National Mineral Collection, Geological Survey of Canada, for his contributions to Canadian mineralogy.

Steacyite is found as radiating crystals, twinned micro to elongated prismatic crystals, and massive material in colors of light to dark brown, beige, green and yellow. It is found as dark-brown twinned micro (sub-milimeter) crystals at the Poudrette Quarry in Canada but as relatively large (to 2 cm), yellow to light brown elongated prismatic crystals in purple Charoite at the Murunskii Massif in Russia.

Steacyite is only found in a few locations worldwide. At the Type Locality (TL) Poudrette Quarry, Mont Saint-Hilaire, Québec, Canada. On Rouma Isle, Los Islands, Guinea. In the Dara-i-Pioz massif, Alai Range, Tien Shan, Tajikistan. At the Murunskii Massif, Chara and Tokko Rivers Confluence, Aldan Shield, Sakha Republic (Saha Republic; Yakutia), Eastern-Siberian Region, Russia.
 

  
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