THE MINERAL NARSARSUKITE

Chemistry: Na2(Ti, Fe)Si4(O, F)11, Sodium Titanium Iron Silicate Fluoride.
Class: Silicates
Subclass: Inosilicates
Uses: Only as mineral specimens and cut as gemstones for gemstone collectors.
Specimens

Narsarsukite is not a well known mineral, but it is a nice collection mineral. It is named for the wonderful mineral locality at Narsarsuk, Greenland, from where the first specimens were described in 1900. The locality is the result of agpaitic pegmatite intrusions, an unusual igneous rock that is high in alkaline metals (such as sodium) and poor in silica. These intrusions also contain a large number of unusual elements such as titanium, fluorine and rare earth metals.

Narsarsukite is also found at Mont Saint-Hilaire, Quebec; another agpaitic pegmatite location. Here is probably the best location for narsarsukite specimens as crystals are relatively large and well formed.

Narsarsukite has been cut as a gemstone, although do not expect to see it available in many jewelry stores. It is cut mostly for gemstone collectors, but is considered attractive. A cut stone of 0.31 carats was cut from the mines of Mont Saint-Hilaire, Quebec and is the largest known narsarsukite gemstone.

Narsarsukite's structure involves double chains of linked silicate tetrahedrons in a tube like arrangement. The chains are actually kinked into a what is best described as a "crankshaft" shape with the kinks going up and down like a crankshaft. The chemistry of narsarsukite may include yttrium, calcium and potassium, but they are not usually significant enough to include in the general formula.

PHYSICAL CHARACTERISTICS:

Color is various shades of yellow, green, pink and brown as well as colorless.
Luster is vitreous or adamantine to dull or greasy.
Transparency: crystals are transparent to translucent.
Crystal System is tetragonal.
Crystal Habits include tabular and prismatic crystals often arranged into sprays and parallel aggregates.
Cleavage is perfect in two directions (prismatic) and good in one direction (basal).
Fracture is uneven to subconchoidal.
Hardness is 6 - 7.
Specific Gravity is approximately 2.6 to 2.8
Streak is white.
Other Characteristics: Index of refraction: 1.601 - 1.614 and 1.632 - 1.647.
Associated Minerals are quartz, microcline, albite, amphiboles, carletonite, lorenzenite, calcite, leucosphenite, natrolite and aegirine.
Notable Occurrences include the type locality at Narsarsuk, Greenland and perhaps the best source of Mont Saint-Hilaire, Quebec, Canada as well as in north-central Montana, USA.
Best Field Indicators: Crystal habit, cleavage, color, associations and localities.