Scapolite was first found in the Mogok District of Myanmar in 1913, which is a relatively unknown new gem species in the 21st century. The English name “Scapolite” originates from the Greek word “Skapos,” which means “column .”It is probably named because the original stone crystals of the Scapolite are primarily short or long columns.
Although there are many colors of Scapolite stone, the stone with cat’s eye effect is more commonly seen in jewelry. The purple Scapolite is similar to amethyst in appearance.
Scapolite is an intermediate member between Marialite and meionite. At present, pure Marialite or meionite has not been found in nature, and it is very rare that any component content exceeds 80%. With the increase of Ca content in the composition, the refractive index, birefringence and density also increase.
Under the microscope, Scapolite usually has tubular inclusions, needle-shaped inclusions, solid inclusions, gas-liquid inclusions, and negative crystals.
Scapolite is produced in calcium-rich regional metamorphic rocks and pegmatites. It develops into intact colorless crystal groups in the interstices of volcanic rocks.
The quality of Scapolite produced in the regional metamorphic rocks is poor, and the quality of Scapolite produced in the contact metamorphic zone between volcanic rocks and limestone is the best.
The Scapolite is vulnerable to weathering and hydrothermal alteration.
It can often be changed into epidote, albite, anorthite, zeolite, mica, etc., and can be changed into kaolin clay during weathering. The origin of the Scapolite is Myanmar, Madagascar, Brazil, India, China, Tanzania and Mozambique, among which the cat’s eye is mainly produced in Myanmar and China.
Basic properties of Scapolite
1) Mohs hardness: 5-6.
2) Cleavage: {100} cleavage is medium, and {110} cleavage is incomplete.
3) Density: 2.50 ～ 2.78g/cm.
4) Optical property: inhomogeneous body, uniaxial crystal, negative optical property.
5) Refractive index: 1.533 ～ 1.607; The birefringence is 0.002 ～ 0.039.
6) Gloss: glass luster.
7) Color: purple-red, pink, orange, yellow, green, blue, colorless, etc.
8) Pleochroism: medium to strong.
9)Transparency: transparent, semi-transparent if there are many inclusions.
10) Special optical effect: It can have cat’s eye effect.
Physical characteristics of Scapolite
The chemical formula of Scapolite is (Na, Ca, K) 4 [Al (AI, Si) Si2O8] 3 (Cl, F, OH, CO3, SO4). Scapolite is a series of continuous solid solutions with end members of Marialite and meionite molecules (Me).
According to the content of Ma and Me, the Scapolite can be subdivided into Marialite, dipyre, Mizzonite and meionite. The common ones in nature are mostly dipyre and Mizzonite.
Types of Scapolite
The name Scapolite originates from the Greek word Skapos (mine, shaft), emphasizing that the mineral is usually short columnar crystalline,
Marialite (MapHaJIHT) is named after Maria, the wife of Ge Lat.
The name Mizzonite (MHIIIIOHHT) originates from the Greek word Meizon (large), emphasizing that its c/a value is greater than that of Scapolite, meaning that it is close to the intermediate component of the Scapolite solid solution series.
The name Meionite (MeHoHHT) originates from the Greek word Meion (small), which emphasizes that the spike of the mineral crystal shape is smaller than that of the associated Vesuvianite, meaning the most calcium-rich Scapolite.
Form:
It belongs to the tetragonal crystal system. The crystal form is columnar, sometimes double cone is developed, but it is often irregular and granular. The {100} cylinder is completely cleaved, and It can find two sets of mutually perpendicular cleavage lines in the cross-section;
Sometimes there are also {110} cleavage (relatively complete) lines oblique to it.
Optical and color: white, gray, sometimes with light-yellow, light-green, light-red; Colorless in the thin slices.
The highest interference color is Class I dark gray to Class III blue. The refractive index and birefringence increased with the increase of the content of the meionite molecules.
The plane parallel to the c-axis is parallel extinction, negative ductility. One axis (-).
Change: generally stable; sometimes it can become mica and calcite.
Occurrence: mainly produced in skarn, symbiotic with garnet, diopside and Vesuvianite; It is also produced in regional metamorphic marble, calcareous schist and amphibolite.
Scapolite is the altered product of plagioclase in the medium basic magmatic rocks. In the pores of volcanic rocks, there are Scapolite crystals.
Main identification features
Raw stone identification
Tetragonal columnar crystal, the perfect crystal is the aggregation of tetragonal columns and tetragonal bipyramids, but the two ends of the crystal are often broken, and there are dense longitudinal lines on the crystal surface.
Finished product identification
The color of Scapolite mainly includes purple, yellow, pink and colorless, and the refractive index and birefringence are different with different colors.
Generally, the refractive index and birefringence of purple Scapolite are low, which are only 1.535~1.545 and the birefringence of 0.004 to 0.009.
The refractive index of other colors of Scapolite is high, sometimes as high as 1.56~1.58, the birefringence is above 0.020, and a few even as high as 0.037.
Most of the Scapolite have typical needle-like inclusions, which can be distinguished from other similar gemstones.
In addition, due to the low hardness, the surface wear resistance is poor.
It is easy to mix with topaz and tourmaline by the naked eye, which can be identified according to the low refractive index and density of Scapolite.
It is also easy to mix with beryl, and they overlap on the same refractive index sequence but can be distinguished according to Scapolite’s high birefringence and cleavage.
Scapolite is also easy to be mixed with symbiotic citrine, amethyst, and various quartz, which can be distinguished by different optical properties.
For example, quartz is positive, while Scapolite is negative.
In addition, the shape of purple Scapolite is very similar to that of amethyst, but the refractive index and birefringence of Scapolite are generally lower than that of quartz.
The cleavage surface of Scapolite can also be seen under the microscope, but quartz has no cleavage.
- It is distinguished from muscovite by its low interference color, negative ductility and uniaxial crystal;
- It is distinguished from plagioclase by its parallel extinction, no bicrystal and uniaxial crystal;
- It is distinguished from pyroxene and colorless hornblende by its low protrusion, different cleavage angle, parallel extinction, negative ductility and uniaxial crystal;
- It is distinguished from Andalusite and wollastonite by its low protrusion and uniaxial crystal.
Scapolite Optimized processing method
Scapolite is generally gray, grayish yellow, grayish green and light yellowish green. Gem grade Scapolite is required to be bright, translucent, transparent, with large crystal particles, and can be processed into 3mm × 4mm raw stone.
As a result, gem-grade Scapolite is rare. Most of the Scapolite on the market has been optimized.
irradiation (producing purple)
Irradiation treatment can make colorless light to yellow Scapolite samples turn purple and yellow, and some samples have brown tones.
The ultraviolet-visible absorption spectrum of the irradiated purple Scapolite has a wide absorption band in the yellow-green region;
The position of the absorption peak in the ultraviolet-visible absorption spectrum of the irradiated yellow Scapolite is basically consistent with that of the natural Scapolite, and the absorption in the blue ultraviolet region is significantly enhanced.
The optimization of jewelry and jade is to make them more beautiful. Most of them have good durability and stability, and are harmless to the body and gems.
The purpose of optimization is mostly to improve color or clarity. The optimized jewelry and jade may not be indicated on the appraisal certificate.
The more common optimization methods are heat treatment, dipping a small amount of colorless oil, and waxing with light, but the standards of different gems may be different.
Conclusion:
The name Scapolite comes from Greek, which means the columnar of minerals. Scapolite belongs to the family of Scapolite in mineralogy. Since 1913, when gem-grade Scapolite was produced in Myanmar, more Scapolite has been continuously discovered.