THE MINERAL SERIES, SCAPOLITE

  • Chemistry: Na4(Al, Si)12O24Cl to Ca4(Si, Al)12O24(CO3, SO4) , Calcium Sodium Aluminum Silicate Carbonate Chloride Sulfate.
  • Class: Silicates
  • Subclass: Tectosilicates
  • Group: Scapolite.
  • Uses: As gemstones and as mineral specimens.
  • Physical Properties
  • Specimens

Scapolite is actually the name of a series between the sodium chloride rich mineral called marialite and the calcium carbonate rich mineral meionite. The structure of scapolite is similar to some feldspathoids in that it is composed of large open spaces in the framework of silicate and aluminum tetrahedrons. These open spaces are large enough to essentially cage the very large ionic groups of either Na4Cl or Ca4CO3. The sulfate ion shown in the formula is typically barely more than a trace, but is found in far greater percentages than the occasional fluorine or hydroxide interlopers in the scapolite structure.

Scapolite forms in metamorphic rocks from the alteration of plagioclase feldspars. The entire scapolite series is analogous to the plagioclase series. If the formula of marialite is written as 3(Na(Al, Si)4O8)NaCl it is clear how well it matches the formula of the sodium rich plagioclase, albite, NaAlSi3O8. A similar look at meionite's formula, 3(Ca(Al, Si)4O8)CaCO3, shows that it too is near three times the formula of anorthite, CaAl2Si2O8. The addition of the extra sodium chloride or calcium carbonate occurs during metamorphism as well as substantial alteration of the structure. Although nearly pure albite and anorthite specimens are sometimes found, pure forms of meionite and marialite are unknown of in nature.

Distinguishing the scapolite minerals from each other is difficult as they differ only slightly in density and index of refraction, increasing in both with increasing calcium content. It is because of this closeness in properties and yet seemingly very different chemistries that scapolite has had its share of pseudonyms. Wernerite was the most common alternate name for the scapolite series, but now it has mostly disappeared from use. A few other names such as mizzonite and dipyre as well as marialite and meionite have been used as names for the entire scapolite series. Now scapolite is a name recognized by most every mineralogist and rock hound the world over.

Scapolite, which is Greek for "shaft", is commonly found in stubby to long prismatic crystals, hence the name. It is tetragonal so that it will commonly have a square or octahedral cross-section. It belongs to a rather exclusive symmetry class that is shared by only two other well known minerals, powellite and scheelite. The symmetry class is called the Tetragonal Dipyramidal Class and is characterized by only having the one primary four fold axis of rotation and a perpendicular mirror plane, denoted as 4/m. Unfortunately, scapolite rarely forms crystals with the complex faces that would be needed to see this unusual symmetry.

As a gemstone scapolite is not well known, but can be very attractive. The color of its gemstones, which is usually a nice yellow to orange, pink or violet, is its best feature as its fire and hardness are somewhat lacking. Less transparent material can often be cut as cabochons that will often exhibit a good Cat's Eye effect or if the "Cat's Eye" is not distinct enough it will show a play of light similar to Moonstone.

PHYSICAL CHARACTERISTICS:

  • Color is most commonly white, colorless, greenish or gray but also yellow, brown, reddish, pink, violet or blue colors are possible.
  • Luster is vitreous on freshly exposed crystals or surfaces but weathering causes a dulling of the luster.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System: Tetragonal; 4/m
  • Crystal Habits include prismatic to stocky crystals terminated by a pyramid. Complete crystals are rare and often the crystals will have distorted shapes with uneven faces.
  • Cleavage is distinct in several prismatic directions producing a splintery almost fibrous appearance in cleaved massive specimens.
  • Fracture is subconchoidal to uneven.
  • Hardness is 5.5 - 6
  • Specific Gravity is 2.5 - 2.7 (average)
  • Streak is white.
  • Other Characteristics: Will often fluoresce either orange, yellow or more rarely red under ultraviolet light and index of refraction varies from 1.54 to 1.60.
  • Associated Minerals include hornblende, the garnet minerals almandine and andradite, actinolite, microcline, pyroxenes, apatite, andalusite, zircon, sphene, diopside and muscovite.
  • Notable Occurrences include Renfrow Co., Ontario; Franklin, New Jersey, Massachusetts and St Lawrence Co., New York, USA; Arendel, Norway; Mount Vesuvius, Italy and Mexico. Gemstone sources are found in Minas Gerias, Brazil; Madagascar, Tremorgio, Switzerland and Burma.
  • Best Field Indicators include color, crystal habit, cleavage surface features, fluorescence and hardness.
SCAPOLITE specimens:
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SCAPOLITE specimen sca-2
$ 115.00
Dims: 2.5" x 0.9" x 0.6" (6.4 x 2.3 x 1.5 cm)
Wt: 1.28 oz. (36.4 g)
Itaquassu, Esprito Santo, Brazil
This Scapolite specimen consists of a single crystal that possesses a partially complete domed termination. Its crystalline form is evident but very indistinct, so that one cannot really see its correspondence to the tetragonal system. Its luster is unusual in that the most exposed surfaces of its prism faces show a duller, almost pearly luster than the pits and pockmarks inherent in its form, which show a bright, vitreous luster. The termination shows considerable wear and a few spots seem to have almost conchoidal tendencies. The other end shows a breakage surface that has undergone obvious partial healing, and has an almost botryoidal texture to it (see the close-up image). The crystal has a pale yellow coloration and is transparent, but its heavily-striated and irregular faces make determination of its clarity very difficult. It does appear to contain many small, dark inclusions, though.
no photo
sca-2 ($115.00)
Itaquassu, Esprito Santo, Brazil
SCAPOLITE specimen sca-3
$ 175.00
Dims: 0.7 x 0.4 x 0.4" (1.8 x 1.0 x 1.0 cm)
Wt: 12.4 g w/ specimen box
Tanzania
A single Scapolite crystal comprises this specimen. It is in near-perfect condition, showing no visible damage, and has excellent though odd tetragonal prismatic form. The crystal actually looks a bit like apatite, as it appears to have 9 detectable prism faces. Its four-sided pyramidal termination also appears to be three-sided upon first glance, as one face is extremely small. All edges are well-defined, however, and all faces are clean, though the prism faces are heavily striated. It has a moderately pale yellow coloration and a pearly luster, and is transparent and mostly quite clear; several small internal fractures are concentrated around its base, however. There is no host rock of any sort present, and the crystal is affixed inside a plastic specimen box with a hot-glue. One could conceivably cut a stone out of this crystal, though it makes a wonderful specimen.
no photo
sca-3 ($175.00)
Tanzania
SCAPOLITE specimen sca-4
$ 30.00
Dims: 1.8 x 0.1 x 0.1" (4.6 x 0.3 x 0.3 cm)
Wt: 9.6 g w/ specimen box
Tremorgio, Switzerland
This specimen represents one of only a few pieces that we have from Switzerland. It consists of a single Scapolite crystal that is in excellent condition and has good tetragonal prismatic form that is almost needle-like. Its edges are moderately well-defined, its faces are striated but clean, and its termination is flat and basal-oriented- it may be the result of breakage that partly healed over. The crystal has a very subtle pale yellow coloration and a pearly luster, and is transparent and very clear. There is no host rock present, and it is hot-glued into a plastic specimen box.
no photo
sca-4 ($ 30.00)
Tremorgio, Switzerland
SCAPOLITE specimen sca-5
$ 70.00
Dims: 4.6 x 3.6 x 1.9" (11.7 x 9.1 x 4.8 cm)
Wt: 1 lb., 5.5 oz. (610 g)
Lady Smith Quarry, Bancroft, Ontario, Canada
This small cabinet specimen is made up mostly of massive Scapolite, a mineral also known as Wernerite. It is distinguishable as a dull, pale yellow massive material in the piece, but is easily visible when put under longwave UV light, as it glows a bright yellow. It appears to have some crystalline tendencies but shows no definite form, and has a pearly luster.
no photo
sca-5 ($ 70.00)
Lady Smith Quarry, Bancroft, Ontario, Canada
SCAPOLITE specimen sca-6
$ 32.00
Dims: 3.8 x 2.1 x 2.1" (9.6 x 5.3 x 5.3 cm)
Wt: 8.7 oz. (246 g)
Lady Smith Quarry, Bancroft, Ontario, Canada
This hand-sized, massive Scapolite (aka Wernerite) piece shows some visible crystalline tendencies, but no actual form. It has a dull white color with a hint of gray and a pearly luster, and is opaque. When viewed under longwave UV light, however, it glows with a bright yellow coloration.
no photo
sca-6 ($ 32.00)
Lady Smith Quarry, Bancroft, Ontario, Canada
SCAPOLITE specimen sca-7
$ 25.00
Dims: 2.1 x 1.1 x 0.8" (5.4 x 2.9 x 2.1 cm)
Wt: 1.38 oz. (39.2 g)
Lady Smith Quarry, Bancroft, Ontario, Canada
I think that this small hand specimen of massive Scapolite (aka Wernerite) strongly resembles some feldspar pieces that I have seen- it appears to have a warped crystal form and has a dull cream coloration and some possible rust-staining. Its luster is waxy at best, and it is completely opaque. Portions of it glow a bright yellow under longwave ultraviolet light, however, betraying its true identity.
no photo
sca-7 ($ 25.00)
Lady Smith Quarry, Bancroft, Ontario, Canada
SCAPOLITE specimen sca-8
$ 115.00
Dims: 0.8 x 0.4 x 0.4" (2.1 x 1.1 x 1.1 cm)
Wt: 4 g
Tanzania
This thumbnail piece consists of a single, loose Scapolite crystal that is in excellent condition, showing no damage. Its tetragonal prismatic form is also extremely good, and it is capped with a shallow pyramid that is quite off-center. Its pale yellow color, vitreous luster are standard for the locality, and its high transparence is marred slightly by a few inclusions and internal fractures.
no photo
sca-8 ($115.00)
Tanzania
SCAPOLITE specimen sca-10
$ 65.00
Dims: 0.9 x 0.3 x 0.3" (2.2 x 0.8 x 0.7 cm)
Wt: 2 g
Tanzania
This loose Scapolite shows almost no damage and has an excellent tetragonal prismatic form with a shallow pyramidal termination. It is extremely clear- only a few very small inclusions are present near its base- and it has a pale yellow color and a pearly-to-vitreous luster.
no photo
sca-10 ($ 65.00)
Tanzania
SCAPOLITE specimen sca-9
$ 80.00
Dims: 0.7 x 0.4 x 0.3" (1.9 x 1.0 x 0.8 cm)
Wt: 3 g
Tanzania
This single, loose Scapolite crystal is in excellent condition, showing no damage, and has equally excellent tetragonal prismatic form capped with a shallow pyramid. It has a pale yellow color and vitreous luster, and is transparent and very clear, containing only a few small, shallow internal fractures.
no photo
sca-9 ($ 80.00)
Tanzania
SCAPOLITE specimen sca-11
$ 25.00
Dims: 2.55x0.46x0.35" (6.48x1.18x0.88cm)
Wt: 0.44oz (12.5g)
Lavra da Laranja, Aracruz, Espirito Santo, Brazil
This is a scapolite crystal from an area in Brazil that has produced many such crystals. Superficially, it has a pale yellow color, deep striations, and a surface texture (or coating) that renders the crystal translucent. Examination with a loupe reveals that the coating is restricted to the surface and that the interior is highly transparent. Indeed, the crystal looks a lot like a yellow spodumene, in that it has the surface texture and crystal terminations common in kunzite crystals, and it is colorless from the side, but very yellow when viewed along the crystal axis (it appears strongly pleochroic). So, is it scapolite (as identified by the mine), or possibly a rare yellow spodumene?
no photo
sca-11 ($ 25.00)
Lavra da Laranja, Aracruz, Espirito Santo, Brazil
SCAPOLITE specimen sca-12
$ 60.00
Dims: 0.75x0.57x0.45" (1.90x1.44x1.15cm)
Wt: 24.5ct (4.9g)
Dodoma, Tanzania
This is a prismatic crystal of yellow, transparent scapolite. It has a somewhat distorted and unusual appearance, in that the octahedral cross section is incomplete (one face is tiny, another is missing) showing just six sides, and the roof termination is offset - none of the roof edges line up with a face edge. There are barely perceptible striations on the crystal's sides, and the termination has a strong growth pattern which hints of striations and results in a dull luster (the sides are vitreous). There are both black and orange inclusions. There is no significant damage, other than to the base where the crystal was separated from its host rock.
no photo
sca-12 ($ 60.00)
Dodoma, Tanzania
SCAPOLITE specimen sca-13
$ 35.00
Dims: 0.66x0.48x0.37" (1.68x1.22x0.93cm)
Wt: 16.1ct (3.22g)
Dodoma, Tanzania
This scapolite crystal is a characteristic pale yellow, transparent, and vitreous except for the termination which has a dull appearance. The crystal is prismatic with a distorted cross section: it is a rectangle with each corner flattened to make it eight sided, but one of the corners is drastically flattened to the point that one of the sides has only a minute presence. The termination is roof-shaped. The crystal's sides show mild striations and a little damage and intergrowth with the host matrix.
no photo
sca-13 ($ 35.00)
Dodoma, Tanzania

 


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