Ontario Mineral - Sodalite

Rocks minerals Ontario Sodalite

Chemistry:

Na4Al3(SiO4)3Cl, Sodium Aluminum Silicate Chloride.

Class:

Silicates

Subclass:

Tectosilicates

Group:

Sodalite and feldspathoid groups

Uses:

mineral specimens and ornamental stone

Color:

blue, white, gray, or even green

Luster:

vitreous or greasy

Transparency:

Crystals are transparent to translucent, massive specimens are opaque.

Crystal System:

Isometric; bar 4 3/m

Crystal Habits:

Dodecahedral crystals have been found, usually massive as a rock forming mineral.

Cleavage:

poor, in six directions, but rarely seen

Fracture:

uneven

Hardness:

5.5 - 6.0

Specific Gravity:

2.1 - 2.3

Streak

white

Other Characteristics:

it is the only feldspathoid to give a positive chlorine test when dissolved in a HNO2 dilute solution.

Associated Minerals:

calcite, nepheline, cancrinite and other feldspathoids.

Local Occurance:

Cancrinite Hill, Davis Hill, Davis Quarry, EganChute, Goulding-Keene Quarry, Morrison Quarry, Gutz Farmhackmanite - pink variety of sodalite; fluoresces brilliantly under U.V.C: pink to purple. H: 6(Morrison Quarry, Davis Quarry).

Best Field Indicators:

are color if blue, lack of pyrite association (as in lazurite), hardness and associations.

Description:

Sodalite is a scarce mineral that can be rock forming. Sodalite is named in reference to its sodium content. It is used for carvings and some jewelry pieces. Its light to dark pure blue color is well known in the semi-precious stone trade. Sodalite is a member of the feldspathoid group of minerals. Minerals whose chemistries are close to that of the alkali feldspars but are poor in silica (SiO2) content, are called feldspathoids. As a result or more correctly as a function of the fact, they are found in silica poor rocks containing other silica poor minerals and no quartz. If quartz were present when the melt was crystallizing, it would react with any feldspathoids and form a feldspar.. Localities that have feldspathoids are few but some produce large quantities of sodalite. Sodalite, when not blue, is hard to distinguish from other feldspathoids. It is the only feldspathoid that contains chlorine. Sodalite dissolved in a dilute solution of HNO3 gives a positive chlorine test obtained from some swimming pool test kits.

Chemistry:
MgAlBO4 , Magnesium Aluminum Borate.
Class:
Carbonates
Subclass:
Borates
Uses:
An a gemstone and as mineral specimens.
Color:
greenish brown to brown, sometimes greenish-yellow.
Luster:
vitreous
Transparency:
Crystals are transparent to translucent.
Crystal System:
orthorhombic.
Crystal Habits:
are quite limited to alluvial grains found in gem gravels.
Cleavage:
distinct in two directions.
Fracture:
conchoidal
Hardness:
6.5
Specific Gravity:
approximately 3.5 (slightly above average for translucent minerals)
Streak
white
Other Characteristics:
strongly pleochroic, meaning it may appear to have different colors from different viewing angles.
Associated Minerals:
are other gem gravel minerals such as ruby, sapphire, peridot and garnets.
Local Occurance:
Warwickite Occurrence
Best Field Indicators:
are color, locality, pleochroism and the relatively high hardness, occurs as transparent vitreous grains in irregular masses.

Description:

Sinhalite is rare mineral and known only from the gem gravels in Sri Lanka. It was thought to be a brownish variety of the normally green peridot, the gem variety of olivine. It was first discovered to be a new species in 1952 when an unusually dark brown specimen came under scientific scrutiny. Since then it has been an unusual gemstone, being a member of the borates. Because it is so rare, has few notable characteristics to give it distinction and the not too overwhelming demand for brownish green gemstones; sinhalite has not enjoyed much success on the gemstone markets and is usually sought after only by collectors of rare and unusual gemstones. Sinhalite gets its name from sinhala, the Sanskrit word for the island of Ceylon, now known as Sri Lanka.