THE MINERAL ELPIDITE

Chemistry: Na₂ZrSi₆O₁₅ - 3H₂O, Hydrated Sodium Zirconium Silicate.
Class: Silicates
Subclass: Phyllosilicates
Uses: Only as mineral specimens.
Specimens

Elpidite is another in the long list of unusual mineral that come from agpaitic pegmatite rocks. Agpaitic pegmatite intrusions are unusual igneous rocks that are high in alkaline metals (such as sodium) and poor in silica. These intrusions also contain a large number of unusual elements such as zirconium. Elpidite was first discovered at Narsarsuk, Greenland, from where the first specimens were described in 1932. It is also found at Mont Saint-Hilaire, Quebec; another agpaitic pegmatite location. Mont Saint-Hilaire is undoubtedly the best location for elpidite specimens, as specimens from there form large sprays and interesting aggregates; and some specimens are fluorescent. Elpidite is a rare zirconium silicate mineral that can have a very nice crystal form and provide good specimens for micromounts and even larger cabinet specimens.

PHYSICAL CHARACTERISTICS:

Color is colorless, white, gray, tan to brick-red.
Luster is vitreous, earthy, dull or silky.
Transparency: Crystals are typically opaque to translucent or rarely transparent.
Crystal System is orthorhombic.
Crystal Habits include prismatic or acicular crystals often forming sprays or stibnite-like aggregates. Individual crystals can have sharp pointed terminations
Cleavage is good in two directions (prismatic).
Fracture is splintery or uneven.
Hardness is variable at 5 - 7.
Specific Gravity is approximately 2.5 to 2.6
Streak is white.
Other Characteristics: some specimens fluoresce green or yellow-green under shortwave UV light.
Associated Minerals are calcite, albite, bastnasite, apatite, rutile, pyrochlore, siderite, epididymite, chlorites, natrolite and aegirine.
Notable Occurrences include the type locality at Narsarsuk, Julianehaab district, Greenland and perhaps the best source for collection specimens is Mont Saint-Hilaire, Quebec, Canada. Also found at Langesundfjord, Norway.
Best Field Indicators: Crystal habit, color, cleavage, associations and localities.