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Tilleyite
Current inventory:  0 gems
 

  
Tilleyite is named after Cecil Edgar Tilley (1894 - 1973), Professor of Petrology, Cambridge University, Cambridge, England.

Discovered in 1933;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Ca₅Si₂O₇(CO₃)₂

Calcium Silicate Carbonate

Molecular Weight:

488.58 gm

Composition:

Calcium

41.02 %

Ca

57.39 %

CaO

Silicon

11.50 %

Si

24.60 %

SiO₂

Carbon

4.92 %

C

18.02 %

CO₂

Oxygen

42.57 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/C.09-20

Nickel-Strunz 10th Ed. ID:

9.BE.82

9 : SILICATES (Germanates)
B : Sorosilicates
E : Si₂O₇ groups, with additional anions; cations in octahedral [6] and greater coordination

Related to:

Tilleyite - Killalaite Group

Varieties:

None

Synonyms:

None

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

As subhedral crystals, rounded grains, and irregular plates.

Twinning:

On {100}, simple; rarely, lamellar

Physical Properties

Cleavage:

Perfect on {201}; poor on {100} and {010}; very poor on {001}

Fracture:

No data

Tenacity:

Brittle

Moh's Hardness:

No data

Density:

2.82 - 2.84 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

White, Colorless in thin section

Transparency:

Translucent to Transparent

Luster:

Vitreous, Dull

Refractive Index:

1.612 - 1.654  Biaxial (+)

Birefringence:

0.0370 - 0.0400

Dispersion:

Perceptible; r < v

Pleochroism:

None

Occurances

Geological Setting:

In the contact metamorphic zone between igneous rocks and limestones, formed at low pressure and high temperature.

Common Associations:

Merwinite, Spurrite, Gehlenite, Vesuvianite, Grossular, Wollastonite, Thaumasite, Fluorite, Calcite

Type Locality:

Crestmore quarries, Crestmore, Riverside Co., California, USA

Year Discovered:

1933

View mineral photos:

Tilleyite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Tilleyite is a rare calcium silicate carbonate mineral that is rarely (if ever) transparent but may occassionally be found as small white translucent crystals that can make attractive gems for collectors of the unusual. It is always white by itself but may appear pale bluish-white when associated with blue Calcite at the type locality of Crestmore, Riverside County, California. The best location for gem quality crystals is from Redcap Creek, Queensland, Australia.

Locations for Tilleyite include the type locality of Crestmore, Riverside County, California; North Peak, Iron Mountains, Sierra County, New Mexico; and near Helena, Lewis and Clark County, Montana, USA. In Ireland, at Barnavave, near Carlingford, County Louth. From near Kilchoan, Ardnamurchan, Argyllshire, and Camas Mòr, Isle of Muck, also on the Isles of Skye and Rhum, Scotland. From the Güneyce-Ikizdere area, Trabzon Province, Turkey. In Russia, from near Anakit Creek, at the mouth of the Lower Tunguska River, central Siberia, and several other less-well-defined localities. At Kushiro, Hiroshima Prefecture, and the Akagané mine, Iwate Prefecture, Japan; and from Redcap Creek, Queensland, Australia.
 

  
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