Images
Formula: Na4(Si20Al4)O48.13H2O
Tectosilicate (framework silicate), dachiardite subgroup,
zeolite group
Crystal system: Monoclinic
Specific gravity: 2.16 measured, 2.17 calculated
Hardness: 4 to 4½
Streak: White
Colour: Colourless, red-orange
Luminescence: Not fluorescent under either long wave or short wave UV
Environments
Volcanic igneous environments
Carbonatites
Localities
At the Francon quarry, Montréal, Québec, Canada, specimens of dachiardite were collected from a pocket of
friable sill rock exposed along the north wall in the lower level of the quarry. The
dachiardite-bearing rock separated into platy fragments that were lined with dachiardite-Na and its
associated minerals. The dachiardite was localised in just one pocket. It is associated with yellowish white
crystalline aggregates of ankerite, light yellow, cone-shaped and
ellipsoidal calcite, white, transparent, sheaf-like and leaf-shaped
quartz, yellow weloganite and
white matted fibres of mordenite. These minerals occur on finely
crystalline, colourless to slightly brownish analcime that forms a lining
on the rock. Mordenite occupies spaces between the
dachiardite-Na tufts and occurs as isolated mounds on the analcime
lining. Colorless transparent plates of albite protrude from the
analcime but are relatively rare. The
analcime also contains inclusions of acicular
aegirine.
Dachiardite-Na occurs as silky white acicular crystals, forming parallel and divergent fibrous bundles of
tiny brittle blades, 1 to 2 mm in length. Less commonly, it exhibits an hourglass structure. Individual crystals
are colourless and the aggregates are white
(CM 19.2.285-289).
Dachiardite-Na from the Francon Quarry -
Image
At the type locality, La Palaccia-Orli di Fassa, Duron Valley, Campitello di Fassa, Trento Province, Trentino-Alto
Adige, Italy, dachiardite-Na occurs as thin, parallel fibres in
basalt, associated with
mordenite and
clinoptilolite subgroup minerals
(Mindat).
Dachiardite-Na from La Palaccia-Orli di Fassa
- Image
Back to Minerals