Jadeite | |
---|---|
General | |
Category | Pyroxene group |
Formula (repeating unit) | NaAlSi2O6 or Na(Al,Fe3+)Si2O6 |
IMA symbol | Jd [1] |
Strunz classification | 9.DA.25 |
Crystal system | Monoclinic |
Crystal class | Prismatic (2/m) (same H-M symbol) |
Space group | C2/c |
Identification | |
Color | Apple-green, emerald-green, bluish green, leek-green, purplish blue, greenish white, white, black, may show green spots, rarely blue or violet; colorless in thin section. Often also banded. |
Crystal habit | Commonly massive, or fibrous, granular; prismatic crystals rare |
Twinning | Single and lamellar twinning on [100] and [001] |
Cleavage | Good on [110] |
Fracture | Splintery |
Mohs scale hardness | 6.5–7 |
Luster | Subvitreous, pearly on cleavages |
Streak | White |
Diaphaneity | Translucent |
Specific gravity | 3.24 to 3.43 |
Polish luster | vitreous to greasy [2] |
Optical properties | Biaxial (+) |
Refractive index | nα = 1.654 – 1.673 nβ = 1.659 – 1.679 nγ = 1.667 – 1.693 |
Birefringence | δ = 0.013 – 0.020 |
Dispersion | r > v; moderate to strong. |
Ultraviolet fluorescence | Dark colors are generally inert. Light green – inert to weak white in long wave, generally inert in short wave; light yellow – inert to weak green in long wave, generally inert in short wave; white – inert to weak in long wave, generally inert in short wave; light purple – inert to weak white or weak brownish red in long wave, generally inert in short wave; some dyed lavender colors – moderate to strong orange in long wave, weaker in short wave [2] |
References | [3] [4] [5] |
Jadeite is a pyroxene mineral with composition Na Al Si 2 O 6. It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4. It is found in a wide range of colors, but is most often found in shades of green or white. Jadeite is formed only in the subduction zones of continental margins, where rock undergoes metamorphism at high pressure but relatively low temperature.
Jadeite is the principal mineral making up the most valuable form of jade, a precious stone particularly prized in China. Most gem-quality jadeite jade comes from northern Myanmar. Jade tools and implements have been found at Stone Age sites, showing that the mineral has been prized by humans since before the beginning of written history.
The name jadeite is derived (via French : jade and Latin : ilia [6] ) from the Spanish phrase "piedra de ijada" which means "stone of the side". The Latin version of the name, lapis nephriticus, is the origin of the term nephrite, which is a different mineral that also shares the common name jade. [7]
Jadeite is a hard, extremely tough, [8] rare mineral of the clinopyroxene family of minerals. [9] Though highly variable in color, [10] it is typically apple-green to emerald-green, or less commonly white or white with spots of green. [9] Occurrences are typically granular or massive; [9] individual crystals are very rare, occurring only as small prismatic crystals in vugs in massive jadeite. [8] Crystals are four-sided or eight-sided in cross section and show perfect cleavage on [110] at angles of 87 and 93 degrees. There is also a rare parting on [100]. The interlocking crystals of massive jadeite help give it its extreme toughness. [11]
Jadeite has a Mohs hardness of 6.5 to 7, slightly less than that of common quartz. [9] Fracture surfaces are sugary in texture, and sparkle from the exposed perfect cleavage on [110]. Jade is relatively dense, with a specific gravity of 3.3 to 3.5 in natural specimens. [9] The specific gravity increases with the iron content, and very pure jadeite has a specific gravity of 3.25. [8] The luster is vitreous, or pearly on exposed cleavage surfaces, and the streak is colorless. [9] Jadeite is translucent to transparent. [8]
Jadeite is characterized by its green color and tough aggregates of compact fibrous crystals. It can be distinguished from nephrite by its vitreous luster on polished surfaces (polished nephrite has an oily luster) [9] and by its higher density and refractive index. Serpentine also has a lower density and refractive index than jadeite. Massive jadeite also characteristically shows a more granular texture than nephrite or serpentinite. [8]
Jadeite has a fusibility of 2.5 (making it moderately easy to fuse with a propane flame) and gives a yellow flame color. [8]
Pure jadeite has the composition NaAlSi2O6 and has the typical clinopyroxene structure. This consists of long chains of silica tetrahedra in which each silicon ion is surrounded by four oxygen ions, with two of the oxygen ions shared with neighboring silica tetraheda. The chains are bonded together by aluminium and sodium ions to form the full three-dimensional structure of a jadeite crystal. The aluminium joins pairs of chains (occupying the so-called M1 site) while sodium joins the paired chains to neighboring paired chains (occupying the so-called M2 site). The resulting crystal structure belongs to the monoclinic system, [9] with space group C2/c. [3]
Pure jadeite has the composition NaAlSi2O6. There is no significant replacement of silicon by aluminium in natural jadeite, and only very limited substitution of ferric iron for aluminium. [9] However, calcium substitutes for up to 20% of the sodium, balanced by substitution of magnesium or ferrous iron for aluminium. [11]
Omphacite is intermediate in composition between jadeite and diopside. [9] However, there is not a true solid solution series, as omphacite has its own structure that is slightly different from either pure jadeite or pure diopside, so that it is separated from either end member by a miscibility gap. [11] Chloromelanite is a dark green variety of jadeite in which some aluminium is replaced by iron, while imperial jade, the most valuable variety of jade, is colored an intense emerald green by traces of chromium. [8]
Jadeite occurs with albite in metamorphic rock of the low-temperature, high-pressure blueschist facies at destructive plate margins. [9] Although it is intermediate in silica content between albite and nepheline, it is not stable under the conditions in which these two minerals are present. Formation of jadeite requires a pressure of 10 to 25 kbar and a temperature of 600 to 1,000 °C (1,100 to 1,800 °F) via the reaction: [9]
+ → | (Reaction 1) |
Jadeite can also form at high pressure via the reaction: [9]
→ + | (Reaction 2) |
At still higher pressure, corresponding to the highest blueschist facies, jadeite reacts with lawsonite to form zoisite and paragonite: [12]
+ → + + + | (Reaction 3) |
Minerals associated with jadeite include: glaucophane, lawsonite, muscovite, aragonite, serpentine and quartz. [9]
Rocks that consist almost entirely of jadeite are called jadeitite. In all well-documented occurrences, jadeitite appears to have formed from subduction zone fluids in association with serpentinite. [13]
Jadeitite is resistant to weathering, and alluvial boulders of jadeitite released from the serpentine-rich environments in which they formed can have weights of up to tons. Raw specimens having Burmese tax stamps or polished slots for evaluating quality are prized by some collectors. [8]
Jadeite's color commonly ranges from white through pale apple green to deep jade green but can also be blue-green (like the recently rediscovered "Olmec Blue" jade), pink, lavender and a multitude of other rare colors. Chloromelanite is a very dark green to black variety. [14] Color is largely affected by the presence of trace elements such as chromium and iron. Its translucence varies from opaque to almost clear. [8] Variations in color and translucence are often found even within a single specimen. [9]
Significant occurrences of jadeite are isolated and rare. [15] It is found exclusively in high-pressure, low-temperature metamorphic rock of continental margins. [9] Here it may be found as pods or veins or as disseminated grains. [11] Deposits are found in Myanmar, the Alps, Russia, [16] California, [9] Japan, [17] and Guatemala. [8] In the Franciscan Complex of California, jadeite is associated with glaucophane, aragonite, muscovite, lawsonite, and quartz. [9] However, occurrences of lapidary quality are almost exclusive to Myanmar. [8] Stream boulders of the Uyu River remain an important source of jadeite. [18]
Jadeite is the dominant mineral of the most desirable variety of jade. [10] This was prized in traditional Chinese culture, where it was worked into a great variety of beautiful ornaments and utensils. [9]
Jadeite was also used by Stone Age peoples for implements and weapons. [9]
Jade received its name, "piedra de ijada" ("stone of the side"), because it was once thought to cure kidney ailments when applied to the side of the body. [8]
Jadeite is one of two minerals recognized as the gemstone jade. The other is nephrite. [19] Occasionally, other minerals such as serpentine or quartz are sold as jade, but the difference can be determined by cleavage and hardness. [20] Jadeite jade is the most valuable form, [8] with the highest-quality material commanding prices well in excess of $200 per carat as of 1994 [update] . [21] Jadeite jade first came into significant use in China only towards the end of the 18th century, as fei tsui. [22]
Jadeite from the Motagua Valley, Guatemala, was used by the Olmec and Maya peoples, as well as the indigenous peoples of Costa Rica. [23]
Unusual colors, like "Olmec blue" jade, which is characterized by its deep blue-green, translucent hue with white flecking, are becoming more highly valued because of its unique beauty and historical use by the Mesoamerican Olmec and also in Costa Rica. [24]
Over 180 axe heads made from jadeitite quarried in northern Italy in the Neolithic era have been found across the British Isles. [25] [26] Because of the difficulty of working this material, all the axe heads of this type found are thought to have been non-utilitarian and to have represented some form of currency or be the products of gift exchange. [27]
A great many jadeite beads and axe heads as well as the remains of jadeite workshops from the Neolithic era have been uncovered in Itoigawa, Japan. These beads and axes were traded throughout Japan and the Korean Peninsula and were produced by the world's oldest known jadeite-using culture, centered on the Itoigawa region. [28] [29]
Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks generally indicates metamorphism deep in the Earth's crust. Kyanite is also known as disthene or cyanite.
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.
Plagioclase ( PLAJ-(ee)-ə-klayss, PLAYJ-, -klayz) is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or "record-groove" effect.
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula XY(Si,Al)2O6, where X represents calcium (Ca), sodium (Na), iron or magnesium (Mg) and more rarely zinc, manganese or lithium, and Y represents ions of smaller size, such as chromium (Cr), aluminium (Al), magnesium (Mg), cobalt (Co), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V) or even iron. Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of silica tetrahedra. Pyroxenes that crystallize in the monoclinic system are known as clinopyroxenes and those that crystallize in the orthorhombic system are known as orthopyroxenes.
Actinolite is an amphibole silicate mineral with the chemical formula Ca2(Mg4.5–2.5Fe2+0.5–2.5)Si8O22(OH)2.
Jade is an umbrella term for two different types of decorative rocks used for jewelry or ornaments. Jade is often referred to by either of two different silicate mineral names: nephrite, or jadeite. Nephrite is typically green, although may be yellow, white or black. Jadeite varies from white or near-colorless, through various shades of green, to lavender, yellow, orange, brown and black. Rarely it may be blue. Both of these names refer to their use as gemstones, and each has a mineralogically more specific name. Both the amphibole jade (nephrite) and pyroxene jade are mineral aggregates (rocks) rather than mineral species. Nephrite was deprecated by the International Mineralogical Association as a mineral species name in 1978. The name "nephrite" is mineralogically correct for referring to the rock. Jadeite, is a legitimate mineral species, differing from the pyroxene jade rock. In China, the name jadeite has been replaced with fei cui, the traditional Chinese name for this gem that was in use long before Damour created the name in 1863.
The chlorites are the group of phyllosilicate minerals common in low-grade metamorphic rocks and in altered igneous rocks. Greenschist, formed by metamorphism of basalt or other low-silica volcanic rock, typically contains significant amounts of chlorite.
Blueschist, also called glaucophane schist, is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures, approximately corresponding to a depth of 15–30 km (9.3–18.6 mi). The blue color of the rock comes from the presence of the predominant minerals glaucophane and lawsonite.
Aegirine is a member of the clinopyroxene group of inosilicate minerals. It is the sodium endmember of the aegirine–augite series. It has the chemical formula NaFeSi2O6, in which the iron is present as the ion Fe3+. In the aegirine–augite series, the sodium is variably replaced by calcium with iron(II) and magnesium replacing the iron(III) to balance the charge. Aluminum also substitutes for the iron(III). Acmite is a fibrous green-colored variety.
Clinozoisite is a complex calcium aluminium sorosilicate mineral with formula: Ca2Al3(Si2O7)(SiO4)O(OH). It forms a continuous solid solution series with epidote by substitution of iron(III) in the aluminium (m3 site) and is also called aluminium epidote.
The use of jade in Mesoamerica for symbolic and ideological ritual was highly influenced by its rarity and value among pre-Columbian Mesoamerican cultures, such as the Olmec, the Maya, and the various groups in the Valley of Mexico. Although jade artifacts have been created and prized by many Mesoamerican peoples, the Motagua River valley in Guatemala was previously thought to be the sole source of jadeite in the region.
Omphacite is a member of the clinopyroxene group of silicate minerals with formula: (Ca, Na)(Mg, Fe2+, Al)Si2O6. It is a variably deep to pale green or nearly colorless variety of clinopyroxene. It normally appears in eclogite, which is the high-pressure metamorphic rock of basalt. Omphacite is the solid solution of Fe-bearing diopside and jadeite. It crystallizes in the monoclinic system with prismatic, typically twinned forms, though usually anhedral. Its space group can be P2/n or C2/c depending on the thermal history. It exhibits the typical near 90° pyroxene cleavage. It is brittle with specific gravity of 3.29 to 3.39 and a Mohs hardness of 5 to 6.
Lawsonite is a hydrous calcium aluminium sorosilicate mineral with formula CaAl2Si2O7(OH)2·H2O. Lawsonite crystallizes in the orthorhombic system in prismatic, often tabular crystals. Crystal twinning is common. It forms transparent to translucent colorless, white, pink, and bluish to pinkish grey glassy to greasy crystals. Refractive indices are nα = 1.665, nβ = 1.672 – 1.676, and nγ = 1.684 – 1.686. It is typically almost colorless in thin section, but some lawsonite is pleochroic from colorless to pale yellow to pale blue, depending on orientation. The mineral has a Mohs hardness of 7.5 and a specific gravity of 3.09. It has perfect cleavage in two directions and a brittle fracture. Not to be confused with Larsonite, a fossiliferous jasper mined in Nevada.
Jadeite is presumed one of the most precious materials of Pre-Columbian Costa Rica. It, along with other similar-looking greenstones were cherished and worked for years. Jadeite was used to decorate the body and was presumably a symbol of power.
Jadeitite is a metamorphic rock found in blueschist-grade metamorphic terranes. It is found in isolated metasomatically altered rock units within serpentinite associated with subduction zone environments. Jadeitite consists almost entirely of the pyroxene mineral jadeite and is typically mined as a source of the ornamental rock or gemstone, jade. Occurrences include Myanmar, Guatemala, Japan, Kazakhstan and in the Coast Ranges of western North America.
Sierra de las Minas is a mountain range in eastern Guatemala which extends 130 km west of the Lake Izabal. It is 15–30 km wide and bordered by the valleys of the Polochic River in the north and the Motagua River in the south. Its western border is marked by the Salamá River valley which separates it from the Chuacús mountain range. The highest peak is Cerro Raxón at 3,015 m. The Sierras (Chuacús) rich deposits of jade and marble have been mined for centuries. The small scale mining activities explain the name of the mountain range.
Greenstone is a common generic term for valuable, green-hued minerals and metamorphosed igneous rocks and stones which early cultures used in the fashioning of hardstone carvings such as jewelry, statuettes, ritual tools, and various other artifacts. Greenstone artifacts may be made of greenschist, chlorastrolite, serpentine, omphacite, chrysoprase, olivine, nephrite, chloromelanite among other green-hued minerals. The term also includes jade and jadeite, although these are perhaps more frequently identified by these latter terms. The greenish hue of these rocks generally derives from the presence of minerals such as chlorite, hornblende, or epidote.
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in the geological history of the area. The boundaries between facies are wide because they are gradational and approximate. The area on the graph corresponding to rock formation at the lowest values of temperature and pressure is the range of formation of sedimentary rocks, as opposed to metamorphic rocks, in a process called diagenesis.
Clinopyroxene thermobarometry is a scientific method that uses the mineral clinopyroxene to determine the temperature and pressure of the magma when the mineral crystalized. Clinopyroxene is found in many igneous rocks, so the method can be used to determine information about the entire rock. Many different minerals can be used for geothermobarometry, but clinopyroxene is especially useful because it's a common phenocryst in igneous rocks and easy to identify, and the crystallization of jadeite, a type of clinopyroxene, implies a growth in molar volume, making it a good indicator of pressure.
Antigorite is a lamellated, monoclinic mineral in the phyllosilicate serpentine subgroup with the ideal chemical formula of (Mg,Fe2+)3Si2O5(OH)4. It is the high-pressure polymorph of serpentine and is commonly found in metamorphosed serpentinites. Antigorite, and its serpentine polymorphs, play an important role in subduction zone dynamics due to their relative weakness and high weight percent of water (up to 13 weight % H2O). It is named after its type locality, the Geisspfad serpentinite, Valle Antigorio in the border region of Italy/Switzerland and is commonly used as a gemstone in jewelry and carvings.