The name Idocrase (Vesuvianite) is originally from Greek, meaning “form” and “mixing” because its crystal shape is similar to other minerals. But in mineralogy, the name of Idocrase is Vesuvianite, which is said to be related to the Vesuvius volcano. Some people also call its large green variety California stone, or “California jade,” which is a common gem and jade raw material.
- Mohs hardness: 6~7
- Cleavage:{ 110} Incomplete cleavage.
- Density: 3.34~3.44g/cm.
- Optical property: inhomogeneous body, uniaxial crystal, negative optical property, and a few positive optical properties
- Refractive index: 1.701 ～ 1.736, birefringence: 0.001 ～ 0.006.
- Gloss: glass luster.
- Color: yellow, green, brown, light blue, rose, etc.
- Pleochroism: weak.
- Transparency: transparency.
- Occurrence: It occurs in the contact zone between magmatic rock and limestone and is one of the minerals that make up the skarn.
What is Idocrase?
Idocrase is a complex calcium-magnesium-iron-aluminum silicate mineral, also called ” Vesuvianite,” because it was found in crystalline limestone and volcanic eruption in the Vesuvius region of Italy in the early stage.
Idocrase belongs to the tetragonal crystal system, and the crystal is short columnar, tetragonal bipyramid, and plate-shaped. It is transparent to translucent, glassy to greasy luster.
The colors are mainly green and yellowish brown, and also gray, yellowish green, yellow, maroon, etc.
Yellow-green and yellow-brown high-quality transparent gem crystal, mainly produced in Italy and Kenya.
Canada produces light green and bright yellow crystals, while Pakistan produces green crystals.
Transparent crystals are usually cut and ground into faceted gemstones, which are generally 1~3 carat in size.
California produces green, yellow, and yellowish-brown compact blocks with fine textures, and slightly transparent. It is called “California jade” in the gem industry and is a good material for carving.
Basic Properties of Idocrase
The chemical composition of Idocrase (Vesuvianite) is Ca10Mg2Al4 [Si2O7] 2 [SiO4] 5 (OH) 4. The substitution of components is relatively complex. For example, calcium can be replaced by manganese, sodium, potassium, and uranium; magnesiumFe2+, zinc and copper can replace magnesium; Fe3+, chromium, and titanium can replace aluminum; beryllium can replace silicon, and fluorine can replace OH.
It belongs to the tetragonal crystal system with space group P4/nnc. ao=15.66， co=11.85A。 Z=2. Spectral lines of main powder crystals: 2.75 (100), 2.59 (80), 1.62 (60),2.45（50）.
The single crystal is in the shape of a square short column or a cone with square bipyramid. There are discontinuous longitudinal lines on the cylinder surface, the cross section is square, and the aggregate is granular, rod, fibrous, radial, etc.
Some Idocrases have a syrup-like appearance and contain round crystals. The color is brown, greenish-brown, red, maroon, pink, green, blue-green, blue, yellow, gray, white, or colorless.
Glass luster to resin luster, translucent to transparent. Cleavage 110 is incomplete.
Hardness 6.5~7, generally 6.5;
The density is 3.33~3.43g/cm, generally 3.40g/cm.
Absorption spectrum:
There is a strong absorption band in the blue area (461nm) and a weak band in the green area. Colorless or light green, light brown, sometimes rose, or light purple under transmitted light.
Colored varieties are pleochroic:
It is light brown-yellow to light yellow-brown, brown to gray-brown, yellow-green to colorless, or red-brown to gray.
- The protrusion and roughness are significant.
- Refractive index No=l.705~1.738, Ne=l.701~1.730; It is generally 1.713~1.718.
- The birefringence is 0.004 ～ 0.006, generally 0.005. The interference color is Grade I gray but extremely uneven, and abnormal interference color can be seen. Parallel extinction.
- Uniaxial crystal, negative light.
- Dispersion 0.019.
Where does Idocrase come from?
Idocrase is one of the important “sand kart minerals,”
mainly produced in the Skam in the contact zone between igneous rock and carbonate rock, and often coexist with garnet, diopside, wollastonite, epidote, etc. In addition, also found in crystalline schist, regional metamorphic limestone, nepheline syenite, and other rocks.
The countries in the world that produce gem-grade Idocrase include the United States, Canada, Mexico, the former Soviet Union, Norway, Switzerland, Finland, Italy, Kenya, Sri Lanka, Pakistan, Japan, North Korea, etc.
For example, brown Idocrase crystals are produced in New York State of the United States; California produces a kind of green and yellowish green, slightly transparent to translucent, dense, fine like jade, with a hardness of 6.5 and a density of 3.25-3.32g/cm3. It coexists with almandine and is locally called “California Jade.”
Light green and bright yellow granular and massive Idocrases are produced in Quebec, Canada.
Mexico produces green Idocrase crystals, which co-occur with almandine in the riverbed.
Green Idocrase crystals are produced in the Viluyi River, a tributary of the Lena River in East Siberia of the former Soviet Union, which is called the “Viluyi River Stone.” Norway produces blue Idocrase aggregates with pink Thulite.
- Brown Idocrase crystals are produced in Switzerland.
- Italy produces brown and green Idocrase.
- Kenya produces green and brown transparent Idocrase crystals.
- Idocrase is produced in alluvial placers in Sri Lanka.
- Pakistan produces high-quality green transparent Idocrase crystals.
Idocrase has been found in Shexian County, Hebei Province, Fuzhong County, Guangxi Province, Gejiu County, Yunnan Province, and Wulan County, Qinghai Province.
Idocrase in Shexian County, Hebei Province, occurs in the skarn-type iron deposit, which is located in the contact zone between diorite and Ordovician limestone.
Its crystal is short columnar with square bipyramids, with a diameter of 2~10cm, larger than 15cm. It is brown, greenish-brown, mostly translucent, and a few translucent to transparent, with few cracks, meeting the quality requirements of gemstones.
Basic Metallogenic Law of Idocrase
Idocrase often occurs in the contact zone between igneous rocks, limestone, and dolomite or in alkaline rocks and regional metamorphic rocks.
Anhydrous silicate minerals dominate the early skarn stage. Idocrase is one of the rare hydrous silicate minerals in the early skarn stage, coexisting with garnet, diopside, wollastonite, epidote, etc. Idocrase+quartz+CO2 can be formed from grossular+diopside+wollastonite+calcite in the contact metasomatic zone.
It is generally believed that Idocrase-bearing skarn was formed in the early gasification hydrothermal stage. The former Soviet Union scholars determined by experiments that the thermal stability region of Idocrase is between 560 ℃ and 710 ℃.
Calcareous metasomatism can form Idocrase veins in basic ultrabasic rocks. Idocrase can also be formed in nepheline syenite and regional metamorphic limestone.
How to identify Idocrase
Opaque Idocrase is easy to mix with jadeite and hydrogrossular, while the appearance of transparent crystal is similar to olivine, diopside, epidote, and other gemstones.
Idocrase is rare in the market and rarely used by the jewelry market.
The glassy Idocrase ranges from single transparent crystal to massive opaque agglomerate.
Pakistan produces green transparent Idocrase containing chromium element; Norway produces blue Idocrase containing copper element, and California produces Idocrase with green to yellowish green color and delicate texture, which is called “California Jade.”
Some Idocrase crystals can be seen with banded structures or abnormal interference color, which can be partially dissolved in hydrochloric acid and precipitate colloidal SiO2.
It is easy to mix with semi-transparent to massive opaque grossular, but grossular is homogeneous. Massive Idocrase has a high refractive index different from jadeite’s.
It is also distinguished from nephrite by its characteristic spectral lines, higher refractive index, and higher density.
Process requirements of Idocrase
In terms of arts and crafts, Idocrase crystal is required to be brown or other bright colors, transparent, crack-free, large particle size, and more than 0.6 carats in weight; Brilliant blocks are dense and tough. Faceted gemstones have appeared, such as brown gemstones weighing 10 carats, yellowish brown gemstones weighing 1.71 carats, and green gems weighing 15 carats. Bright, dense, massive Idocrase can be used as jade carving material instead of jadeite.
Differences between Idocrase and Jadeite
Idocrase gem is one of the rare gemstones. The transparent Idocrase gem crystal is very small, and the largest one is only 15 carats (green). The fine-grain Idocrase aggregate is a kind of delicate jade.
Idocrase is green because it contains chromium, brown or pink because it contains titanium and manganese, and blue because it contains copper, etc. The high-quality Idocrase can be processed as a gem.
Main differences
1. The refractive index of Idocrase stone (1.7) is obviously higher than that of jadeite(1.66).
It is difficult to see the grain boundary of the Idocrase stone when it is magnified. While jadeite has a unique granular fiber interwoven structure. Under spectroscope, the absorption band of 465 nm can be clearly seen in Idocrase stone, while the absorption band of 437 nm can be seen in jadeite
2. The infrared spectra of Idocrase stone and jadeite jade are very different; no matter the spectral bands’ number and shape and the absorption band’s wave number characteristics, there are obvious differences.
In particular, there is no oxhydryl in the chemical composition of jadeite because there is no absorption band in the high-frequency range of 3400-3800cm, while Idocrase stone has a strong absorption band in this range due to its light base. This is the key to distinguishing the Idocrase stone from jadeite.
3. The green Idocrase jade is very similar to the high-quality jadeite in terms of color and texture, but the color distribution is even, and the color is light.
Tips:
The jadeite color of Idocrase stone seems to be the original color, the primary color is uniform, and the bottom is generally fine.
In contrast, the jadeite color of jadeite is a secondary color, and the color is uneven in most cases, and the color is distributed along cracks or grain gaps. The bottom is generally thick, usually with a sense of grain.
If the color of a piece of jade is very uniform and the bottom is very delicate, the possibility of jadeite jade is low.
Idocrase stone, after all, is not jadeite. Although their shapes are somewhat similar, their density and hardness are similar, and as long as they are carefully identified, there are still great differences in refractive index and internal structural characteristics.
The infrared spectra and X-ray diffraction patterns of Idocrase stone and jadeite jade are also very different.
Idocrase Healing Property
It is said that Idocrase has a powerful ability, which can provide information for the soul in the flesh and help to experience the past.
Whether this statement is true or not, in many crystal fans’ minds, it is also a stone closely related to spirituality, which can open the mind, eliminate negative thought patterns, and make the spirit more pure.
It is said that the psychological influence of Idocrase also includes: eliminating the sense of bondage and prudence, which helps people extricate themselves from the heavy emotional depression of copper prohibition for a long time;
Gently smooth people’s anger and fear, and bring a sense of security; Encourage people to invent, create, and find new things easily.
It can protect teeth and Enhance the sense of quack, Helping the body absorb and digest the nutrients in food;
Idocrase gemstones collection
The brown faceted gemstones from Italy, collected by the Smithsonian Museum in Washington, USA, weigh 3.5 carats;
The brown gemstones from Kenya, collected by the Calgary Divo Group in Canada, weigh 8.5 carats.
Conclusion:
The English name of Idocrase comes from Greek, which means that the mineral shape is easily confused with other minerals.
It was first found on Mount Vesuvius, so it is also known as Vesuvius Stone. One of the varieties of Vesuvius Stone is produced in California, USA. It is a green, yellowish-green compact massive Idocrase stone, translucent to slightly transparent, fine and soft as jade, so it is also known as “California Jade.”
Idocrase occurs in contact metamorphic crystalline limestone, serpentinite, and contact metasomatic skarn. It can be divided into four categories. The Idocrase produced in California is California jade; the Green Idocrase stone is produced in Norway; the Yellowish brown Idocrase from the United States; Green Idocrase produced in Siberia, Russia, is also produced in Italy, Kenya, Canada, and other places.