THE MINERAL EUCRYPTITE

  • Chemistry: LiAlSiO4, Lithium Aluminum silicate.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Group: Phenakite
  • Uses: Rarely cut as a gemstone, more common as mineral specimens.
  • Specimens

Eucryptite is one of the few silicate minerals that have a trigonal symmetry. This symmetry is far more common among carbonates than among silicates. Eucryptite shares the same symmetry with the emerald green silicate dioptase, phenakite and the fluorescent mineral willemite. Eucryptite belongs to the small Phenakite Group which includes only three minerals; eucryptite, phenakite and willemite. They all have the same basic structure, hence the same symmetry, but different metal ions.

  • Eucryptite's formula is LiAlSiO4.
  • Phenakite's formula is Be2SiO4.
  • Willemite's formula is Zn2SiO4.
Phenakite is the most well crystallized of the three in general, forming the best crystal shapes and the only one consistently cut as gemstones. Willemite is famous for fluorescing a bright green color under UV light and is found in mass at Franklin and Sterling Hill, New Jersey. Eucryptite is rarely cut as a gem and only some specimens fluoresce a pink color, but none the less it can be a interesting mineral for collectors.

PHYSICAL CHARACTERISTICS:

  • Color is usually colorless or white.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System: trigonal; bar 3
  • Crystal Habits include granular grains and massive forms. Some crystals can be well formed with trigonal prisms with rhombohedral terminations. Eucryptite can also replace spodumene forming pseudomorphs.
  • Cleavage in poor in three directions.
  • Fracture is conchoidal.
  • Hardness is 6.5
  • Specific Gravity is approximately 2.67 (average for non-metallic minerals).
  • Streak is white.
  • Other Characteristics: Prism faces striated lengthwise, index of refraction is 1.55 and some specimens fluoresce pink under UV light.
  • Associated Minerals include quartz, micas, feldspars and spodumene.
  • Notable Occurrences include the type locality of Branchville, Fairfield County, Connecticut, USA as well as Harding Mine, Dixon, New Mexico and Parker Mountain, Stafford, New Hampshire, USA and Bikita, Zimbabwe
  • Best Field Indicators are crystal habit, striations, environment and hardness.
EUCRYPTITE specimens:
(hover for more info)
EUCRYPTITE specimen ecr-1
$ 36.00
Dims: 2.0 x 1.6 x 1.0" (5.0 x 4.2 x 2.6 cm)
Wt: 1.6 oz. (44 g)
Londonderry Quarry, Western Australia, Australia
This specimen consists of an irregular, shapeless chunk of massive Eucryptite. It shows no crystal form whatsoever and actually somewhat resembles a piece of feldspar. It has a milky-white color with some colorless patches and is generally dimly translucent, though the colorless areas show some dim transparence. Its luster is generally dull and waxy, though again, the colorless areas tend to show a brighter, nearly vitreous shine. There is no host rock present.
no photo
ecr-1 ($ 36.00)
Londonderry Quarry, Western Australia, Australia
EUCRYPTITE specimen ecr-2
$ 36.00
Dims:2.4x1.9x0.5" (6.1x4.8x1.3 cm)
Wt: 2.4oz. (66g)
Parker Mtn. Mine, Center Stafford, New Hampshire
This is a massive specimen of eucryptite. Only cleavage faces are available for study. There is no matrix with this specimen, but there is a small amount of muscovite mica attached. This specimen fluoresces dark pink in short wave ultraviolet light.
no photo
ecr-2 ($ 36.00)
Parker Mtn. Mine, Center Stafford, New Hampshire
EUCRYPTITE specimen ecr-3
$ 130.00
Dims: 5.8 x 5.5 x 2.5" ( 15.0 x 14.0 x 7.5 cm)
Wt: 4 lbs. 2 oz. (1875g)
Parker Mountain, Stafford, New Hampshire, USA
This specimen is almost entirely eucryptite by weight, although one side is covered by a layer of feldspar and a scattering of mica crystals. Under short-wave ultraviolet, the eucryptite glows a deep and bright red, which does not image well with my camera. The eucrytite is outlined by a thin layer of willemite, which glows an intense green, which ALSO does not show up on this camera. There is no "blue" florescence - the camera has captured the blue reflection of the UV lamp. This is a great specimen for a short-wave UV cabinet.
no photo
ecr-3 ($130.00)
Parker Mountain, Stafford, New Hampshire, USA
EUCRYPTITE specimen ecr-4
$ 90.00
Dims: 5.8 x 4.5 x 2.6" ( 15.1 x 11.5 x 6.7 cm)
Wt: 3 lbs 1 oz. (1390g)
Parker Mountain, Stafford, New Hampshire, USA
Another nice eucryptite specimen which my UV lamp and camera do not do justice to. They actually glow very nicely with a deep red for the eucryptite (the bulk of the specimen), plus an intense green for the scattering of willemite on the specimen. The specimen also contains a great deal of feldspar and mica, plus some unidentified black mineral. Eucryptite is a "must-have" mineral for a florescent specimen collector.
no photo
ecr-4 ($ 90.00)
Parker Mountain, Stafford, New Hampshire, USA
EUCRYPTITE specimen ecr-5
$ 60.00
Dims: 6.4 x 3.5 x 1.1" ( 15.9 x 8.9 x 3.0 cm)
Wt: 6.35 oz. (180g)
Parker Mountain, Stafford, New Hampshire, USA
This specimen has two bands of eucryptite (easily identified by their red glow under shortwave UV), separated by a band of a mineral that looks identical under visible light, but which does not fluoresce. There are several other minerals present, including quartz, feldspar, and mica. The fluorescent image does not show the deep red glow correctly. I did not detect any other florescence.
no photo
ecr-5 ($ 60.00)
Parker Mountain, Stafford, New Hampshire, USA
 

Copyright ©1995-2023 by Amethyst Galleries, Inc.