THE MINERAL PHENAKITE

  • Chemistry: Be2SiO4, Beryllium silicate.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Group: Phenakite
  • Uses: sometimes cut as a gemstone and as mineral specimens.
  • Specimens
Phenakite is a rare beryllium mineral, but it is found so frequently with precious gemstones that its availablity is not in proportion to its rarity. It is found in pegmatitic pockets and is associated with gemstones such as topaz, beryl especially emerald, chrysoberyl and smoky quartz. The name phenakite, or the alternate spelling, phenacite, is from a Greek word meaning deceiver, an allusion to its deceptively similar look to quartz.

Phenakite is one of the few silicate minerals that have a trigonal symmetry. This symmetry is far more common among carbonates than among silicates. Phenakite shares the same symmetry with the emerald green silicate dioptase and the fluorescent and closely related willemite.

Fine crystals of phenakite can be perfectly clear and with good hardness, rarity and lack of good cleavage, although somewhat lacking in color and fire, make good choices for gemstones.

PHYSICAL CHARACTERISTICS:

  • Color is usually colorless or white but can be tinted yellow, brown and pink.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System: trigonal; bar 3
  • Crystal Habits include flatten rhombohedral to almost tabular and typically short prismatic crystals although some prismatic crystals can be rather long. Also lenticular. Twinning is common and forms penetration twins
  • Cleavage in poor in three directions.
  • Fracture is conchoidal.
  • Hardness is 7.5 - 8
  • Specific Gravity is approximately 2.9 - 3.0 (average for non-metallic minerals).
  • Streak is white.
  • Other Characteristics: Prism faces striated lengthwise and index of refraction is approximately 1.66.
  • Associated Minerals are topaz, cassiterite, quartz, calcite, hematite, feldspars, apatite, fluorite, beryl especially emerald, chrysoberyl, bertrandite and some sulfides.
  • Notable Occurrences include sites on the Takowaja River, Ural Mountains, Russia; Minas Gerias, Brazil; Pala, San Diego Co., California; Mt. Antero and Pikes Peak, Colorado, USA and Norway.
  • Best Field Indicators are crystal habit, striations, enviroment and hardness.
PHENAKITE specimens:
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PHENAKITE specimen phe-1
$ 45.00
Dims: 0.6 x 0.3 x 0.3" (1.4 x 0.9 x 0.9 cm)
Wt: 2 g
Mount Antero, Chaffee County, Colorado, U.S.A.
This small thumbnail specimen consists of a single, doubly-terminated Phenakite crystal that is in excellent condition. Its trigonal form is quite good, and shows interpenetration twinning much like that of cinnabar crystals. It is colorless, transparent and moderately clear and has a pearly-to-vitreous luster. Portions of a few tiny crystals erupt from some spots, but these do not amount to more than a few faces. A dusty black material coats small areas on the crystal, but there is no host rock present.
no photo
phe-1 ($ 45.00)
Mount Antero, Chaffee County, Colorado, U.S.A.
PHENAKITE specimen phe-2
$ 45.00
Dims: 1.1 x 0.7 x 0.6" (2.8 x 1.7 x 1.6 cm)
Wt: 7 g
Mount Antero, Chaffee County, Colorado, U.S.A.
Dozens of tiny Phenakite prisms rest on the crystalline muscovite base of this thumbnail piece. The largest of these crystals is 0.3" (8 mm) long and is the easiest to study- it is in excellent condition and has excellent double-terminated trigonal form. Like the others, it is colorless, transparent, clear, and has a vitreous luster. The muscovite base on which the Joaquinites rest is made up of many well-formed, intersecting platelets.
no photo
phe-2 ($ 45.00)
Mount Antero, Chaffee County, Colorado, U.S.A.
PHENAKITE specimen phe-4
$ 90.00
Dims: 0.8 x 0.5 x 0.4" (2.0 x 1.3 x 1.0 cm)
Wt: 3 g
Mount Antero, Chaffee County, Colorado, U.S.A.
This thumbnail specimen consists of a cluster of at least 6 intergrown Phenakite crystals that are in very good condition and reach dimensions of 0.5 x 0.4 x 0.3" (1.2 x 1.0 x 0.7 cm). The largest crystal shows a small spot of damage, but the rest are in excellen shape. All have excellent trigonal prismatic form and are colorless and transparent. They contain many cloudy inclusions, however, and possess a rather dull, pearly-to-greasy luster. A few broken muscovite blades are attached to the cluster, but no other material is present.
no photo
phe-4 ($ 90.00)
Mount Antero, Chaffee County, Colorado, U.S.A.
PHENAKITE specimen phe-6
$ 42.00
Dims: 1.2 x 1.0 x 0.8" (3.0 x 2.5 x 2.0 cm)
Wt: 16 g w/ foam base
Malyshevo Mine, Ekaterinberg, middle Urals, Russia
A single Phenakite crystal rests in the dark, micaceous matrix of this thumbnail piece. The crystal has dimensions of 0.6 x 0.5 x 0.4" (1.5 x 1.3 x 1.0 cm) and is in very good condition, showing almost no damage. Its trigonal prismatic form is somewhat flattened along one axis, but is still well-defined. Its pale yellow color and pearly luster are common for the specie, and it is transparent and moderately clear. The piece is hot-glued to a foam base which fits into a plastic thumbnail box.
no photo
phe-6 ($ 42.00)
Malyshevo Mine, Ekaterinberg, middle Urals, Russia
PHENAKITE specimen phe-7
$ 263.00
Dims: 1.2 x 1.1 x 1.0" (3.0 x 2.8 x 2.5 cm)
Wt: 22 g
Mount Antero, Chaffee County, Colorado, U.S.A.
This thumbnail specimen consists of a few Phenakite crystals, some of which are intersecting, that are scattered through a crystalline muscovite matrix. Most of the crystals are broken or at least lightly damaged, including the largest. This particular crystal measures about 0.6 or 0.7" (1.5 - 1.8 cm) in diameter and is incomplete due to its intersection with another crystal that was since removed. Its trigonal form has a nearly pseudo-dodecahedral appearance and is very well-defined. All are colorless, transparent and dimly to moderately clear, containing many cloudy inclusions. Their faces have a luster that ranges from nearly matte to vitreous. Only a few other, tiny crystals are sufficiently intact to show good form. The surrounding matrix consists of scores of tiny, pseudohexagonal muscovite books that are intergrown.
no photo
phe-7 ($263.00)
Mount Antero, Chaffee County, Colorado, U.S.A.
PHENAKITE specimen phe-8
$ 48.00
Dims: 0.75x0.39x0.39" (1.9x1.0x1.0cm)
Wt: 21.20ct (4.24g)
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This phenakite crystal has an excellent hexagonal shape, with a pyramid termination. There is only a small amount of damage to the tip and several edges. While the phenakite is transparent and nearly colorless (but with a hint of yellow), it has inclusions, or more properly intergrowth with a mineral that is opaque, dull, and has a pink cast.
no photo
phe-8 ($ 48.00)
?
PHENAKITE specimen phe-9
$ 48.00
Dims: 1.09x1.07x0.69" (2.77x2.72x1.75cm)
Wt: 0.67oz (19.0g)
Malyshevo mine, Ural, Russia
This is a single crystal of phenakite, a beryllium silicate mineral. It is roughly hexagonal in shape, with roof shaped edges. It is incomplete, showing only 6 (of a possible 14) faces. It is colorless and transparent, with a rough exterior that makes it difficult to see into the interior, except at a few spots where fractures expose a somewhat vitreous surface. Also, parts of the surface are coated with a thin layer of muscovite crystals.
no photo
phe-9 ($ 48.00)
Malyshevo mine, Ural, Russia
 

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