Tilasite
Current inventory: 0 gems
 

  
Tilasite was named in 1895 by Stens Anders Hjalmar Sjögren in honor of Daniel Tilas (1712-1772), polymath, geologist, mining engineer, vicar of Hammar, director of mines, and regional governor.

Discovered in 1895; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

CaMg(AsO₄)F

Calcium Magnesium Arsenate Fluoride

Molecular Weight:

222.30 gm

Composition:

Calcium

18.03 %

Ca

25.23 %

CaO

Magnesium

10.93 %

Mg

18.13 %

MgO

Arsenic

33.70 %

As

51.70 %

As₂O₅

Oxygen

28.79 %

O

Fluorine

8.55 %

F

8.55 %

F

—

 —  %

F

-O=F₂

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Phosphates; Subclass: Arsenates

Strunz 8th Ed. ID:

7/B.25-30

Nickel-Strunz 10th Ed. ID:

8.BH.10

8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H₂O
H : With medium-sized and large cations, (OH,etc.):RO₄ = 1:1

Related to:

Tilasite Group. Isostructural with Titanite. Durangite-Tilasite Series. Maxwellite-Tilasite Series.

Members of Group:

Tilasite Group: Durangite, Isokite, Kononovite, Lacroixite, Maxwellite, Panasqueiraite, Tilasite 

Varieties:

None

Synonyms:

Fluor-Adelite, ICSD 75618, PDF 2-485

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals equant, may be elongated along [100], flattened on {010}, with complex domatic form development, to 3.5 cm; in subparallel groups, granular, in veinlets, massive.

Twinning:

On {001}, as contact twins

Physical Properties

Cleavage:

Good on {101}; partings on {133}, {102}, {011}

Fracture:

n/a

Tenacity:

Brittle

Moh's Hardness:

5.0

Density:

3.75 - 3.79 (g/cm³)

Luminescence:

May fluoresce pale yellow, pale pinkish orange, dark red under SW UV.

Radioactivity:

Not Radioactive

Other:

Piezoelectric. Easily soluble in HCl or HNo3.

Health Warning:

Contains arsenic - always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest.

Optical Properties

Color:

Milky white, gray, violet-gray, rose-red, olive-green, apple-green; colorless or pale green in transmitted light

Transparency:

Translucent

Luster:

Resinous, vitreous on cleavages

Refractive Index:

1.640 - 1.675  Biaxial ( - )

Birefringence:

0.035

Dispersion:

Relatively weak, slight; r < v

Pleochroism:

None

Occurances

Geological Setting:

Typically in metamorphosed manganese or zinc deposits containing arsenic.

Common Associations:

Manganoan Diopside, Manganberzeliite, Svabite, Allactite, Pyroaurite, Dixenite, Bergslagite, Hematite, Calcite, Barite (Långban, Sweden); Spessartine, Braunite, Barite, Quartz (Kajlidongri, India); Friedelite, Willemite, Barite (Sterling Hill, New Jersey, USA).

Common Impurities:

None

Type Locality:

Långban, Filipstad, Värmland, Sweden

Year Discovered:

1895

View mineral photos:

Tilasite Mineral Photos and Locations

Unusual Gem Categories

Fluorescent Gems, Piezoelectric Gems

More Information

Mindat.org
Webmineral.com

Tilasite is a rare fluor-arsenate mineral that is a member of the Tilasite Group of minerals that also includes Durangite among others. Tilasite is often found as translucent reddish-brown to pale rose-red granular microcrystals in veins. It is an interesting mineral in that it is a Piezoelectric and fluorescent mineral. Piezoelectricity is the ability of some mineral crystals to generate a voltage in response to applied mechanical stress. Tilasite may fluoresce pale yellow, pale orange or dark red under SW UV light. If you place your cursor over the picture above you will see the orange fluorescence of Tilasite under shortwave UV light. Tilasite specimens found at Långban, Filipstad, Värmland, Sweden may be associated with another fluorescent arsenate mineral, Svabite.

Tilasite was named in 1895 by Stens Anders Hjalmar Sjögren in honor of Daniel Tilas (1712-1772), polymath, geologist, mining engineer, director of mines, and regional governor from Stockholm, Sweden.

Tilasite distribution: from Långban, Filipstad, Värmland, Sweden. In Switzerland, from the Falotta mine, Oberhalbstein, Graubünden, and on the west flank of Cherbadung [Pizzo Cervandone], Binntal, Valais. On the east flank of Pizzo Cervandone, Alpe Devero, Val d’Aosta, Piedmont, and at Val Strona, Ossola, Italy. From the Urupskoye copper deposit, northern Caucasus Mountains, Russia. At Sailauf, northeast of Aschaffenburg, Bavaria, Germany. From near Nežilovo, Macedonia. At Kajlidongri, Madhya Pradesh, India. From Guettera, Algeria. In the Puttapa zinc deposit, near Beltana, South Australia. In the USA, at Sterling Hill, Ogdensburg, Sussex County, New Jersey; from the White Tail Deer mine, Bisbee, Cochise County, Arizona; in the Monticello tin district, Sierra County, New Mexico.
 

  
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