28.74 ct Yellow Scapolite (Tanzania)                                  2.56 ct Purple Scapolite (Tanzania)

Introduction:  Scapolite certainly fits into that category of rare collector stone that is becoming part of the jewelry landscape.  It is not well known by the public but is nonetheless a desirable and attractive gem material.  The name is from the Greek word skapos (shaft) due to the stumpy nature of the crystals.  Scapolite is a group of closely related species comprising a solid solution series ranging from marialite, the sodium rich end member, Na4Al3Si9O24Cl to the calcium rich end member known as meionite, Ca4Al6Si6O24(CO3, SO4).  Mizzonite and wernerite are intermediate members although according to mindat.org, the name wernerite was rejected by the IMA as a valid species.  Distinction between the two end members and along the series is virtually impossible without chemical analysis and therefore gemstones are normally referred to as scapolite.

Colors, Localities and Stone Sizes:  Colors range from colorless to various shades of yellow, as well as purple and rarely pink. Over the years, gemmy scapolite has been found in many countries including Burma, Brazil, Tanzania, Afghanistan, Sri Lanka and Canada.  Today, yellow is the most common in commercial quantities with sizes up to 10 carats readily available, originating in Tanzania.  Purple gems are a distant second with sizes up to 3 carats with rapidly decreasing availability in larger sizes.  Tanzania was considered the source for purple material and a few stones still do trickle from the locality but the bulk is from Badakhshan, Afghanistan in sizes mostly l carat or less.  Colorless material is usually from Sri Lanka or Burma as well as from a recent find (2005) in Afghanistan producing colorless material that fluoresces bright orange-yellow in LW and will also exhibit a blue tenebrescence after 15 minutes exposure to SW. Sizes are rarely over 1 carat.  A new locality in Nunavut, Canada (2008) is producing a light yellow to colorless scapolite that fluoresces so intensely in LW that it can be viewed without dimming any room lighting.  Some of the Canadian material also exhibits tenebrescence.  Sizes are mostly under 2 carats.  Cat’s eye material is rather rare in purple and pink and more common in the colorless material from Canada or Sri Lanka.

1.12 ct Scapolite (Afghanistan) before and after SW-UV

1.12 ct Scapolite (Canada) normal lighting and LW-UV fluorescence

Refractive Index:  1.550-1.564 (+0.015, -0.014)  The refractive index increases with increasing amounts of calcium.
Birefringence:  0.004-0.037  The birefringence increases with an increase in refractive index.
Optic Character:  Doubly Refractive, Uniaxial Negative
Dispersion:  0.017
Pleochroism:  purple and violet stones: moderate to strong blue and blue-purple; yellow stones: weak to moderate orange-yellow and yellow
Specific Gravity:  2.68 (+0.06, -0.08)
Hardness:  6 - 6.5
Crystallography:  Scapolite forms in the tetragonal system with prismatic crystals.
Durability:  Fair                                                            It is best to avoid the ultrasonic and steamer as the sudden change in temperature may lead to fracturing due to thermal shock.  It is also readily attacked by acids.
Cleavage:  The cleavage of scapolite is imperfect but distinct in two directions, {100} and {110}.  It presents no problems during faceting.
Commonly Confused With: Scapolite is most often misidentified as orthoclase, labradorite, quartz or beryl.  Scapolite can be separated from orthoclase and/or labradorite by carefully noting optic character during refractive index readings as the optic character of both orthoclase and labradorite is biaxial.  The quartz varieties amethyst and citrine are uniaxial as is scapolite but with a positve sign while scapolite is negative.  In addition, quartz will generally show a bulls-eye optic figure while scapolite has a typical uniaxial figure.  Like scapolite, beryl is also uniaxial negative but when the refractive index of scapolite is as high as it is in beryl, the birefringence is much higher in scapolite than beryl.
Cause of Color:  color centers
Spectral:  Purple and violet stones often show lines at 6630 and 6520 as well as broad absorption between 5370 and 5970 and total absorption below 4100.  The spectra of yellow scapolite is not distinctive.
Enhancements:  There are several references in the literature as well as online that purple scapolite is sometimes heated to improve color.  The author is unfamiliar with heating as an enhancement but irradiation of colorless or yellow scapolite will produce a purple shade.  The irradiated color is often with a noticeable brown overtone and for all intents and purposes is unstable, fading rapidly in all light sources.  Since the irradiation product is unstable, the prevalence of treatment is not common.

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