Dunite

Classification：Igneous Rock

An ultrabasic intrusive rock, almost all composed of olivine (>90%), containing a small amount of chromite and magnetite, which is abundant in the mantle and is relatively small on the land.

Dunite is one of the ultrabasic intrusive rocks. All or almost entirely composed of olivine (90-100%), dense and hard, because of its first discovery in DunMountain in New Zealand, so it is also known as Dunite.

Brief introduction:
Dunite is a kind of ultrabasic intrusive rocks, all or almost entirely composed of olivine (90%-100%), containing a small amount of pyroxene and other minerals, but the latter (0-10%), often contains chromite, magnetite, ilmenite, pyrrhotite and natural platinum. Fresh Dunite often shows olive green, yellow green or brown green. Hypautomorphic granular structure or granular mosaic structure, massive structure, usually with sideronitic texture rich in iron minerals. Dunite is easy to occur altered serpentinization. Fresh and non serpentinite is rare. It often forms complex with peridotite, pyroxenite and gabbro. In New Zealand, Deng found that due to it, first, Deng Niyan (dunite). More fresh Dunite is the mantle plume xenoliths. The remaining Tibet Champlain rock and Shaanxi Shangnan Songshugou ultramafic intrusion.

Lithofacies study of Dunite:
The Dunite system is formed by different proportions of orthopyroxene, cable-clinopyroxene and olivine. These ores change into symbiotic and serpentine after hydrothermal action, forming talcum. Mineral particles are of medium size and large size. They are monodisperse. They are honeycomb like structures in primary minerals and develop into two symbiosis. The following minerals and compositions were determined by petrographic and geochemical methods.
(1) Masateru stone, according to the classification of enstatite, and contains trace amounts of Ca, Cr and Mn;
(2) the clinopyroxene is classified as diopside according to its composition and contains trace amounts of Ti, Fe and Na.
(3) olivine is classified as olivine containing solid solution (Mg2+-Fe2+) and contains trace Al.
(4) spinel, according to composition, is classified as spinel, showing solid solution formed between iron spinel and magnesia chromite.
(5) non transparent minerals, usually magnetite and small ilmenite.

Serpentine Dunite:
In recent years, an ancient jade article appeared in the collection area. Its main body color is pale yellow green, dark green, and its surface is whitening. This "ancient jade" is mostly large, small 20cm to 30cm, larger than 80cm. As the main character, animal, jade, incense and other shape, its shape and ornamentation is fabricated. The jade materials used are also very special, which are quite different from traditional jade (nephrite, Xiuyu, Dushan jade and Lantian jade). It is said that the transaction price is less than a few thousand yuan, and tens of thousands of yuan. It is also useful for the life box made of this jade material. It has fine texture, beautiful color, natural shape, smooth sculpt and sculpture, and it is a kind of high-grade funeral products .

This special jade material is dense, massive and transparent opaque natural rock. The overall color of jade is yellow green, dark green, careful observation, is composed of grayish yellowish white and yellow green two parts. The yellow and yellow white of the jade is usually the main body, the yellow green part is mainly distributed in the net pulse, and the part is mass distribution. As the relative content of the two parts is different, with the increase of the yellow green part, the whole color changes from the yellow green to the dark green. Partial white spots, veined veins and masses are seen. The fracture of the jade material is serrated, the section is waxy to oil and luster, and the polished surface is weak glass luster. Heterogeneous aggregates, ultraviolet (long and short wave) fluorescence inertness, Charles filter without reaction, Mohs hardness 4~5, density 2.88g/cm3. The main body of the jade material does not react with (1+1) HCl, and drops (1+1) HCl bubbles at local white spots, clumps and veins.

This special jade material is composed of forsterite and chrysotile. Its total content is over 95%. According to the relationship between the structural structure of the rock and the metasomatism between the two minerals, the peridotite is metasomatism in varying degrees by the serpentine, and the actual mineral amount of olivine should not be less than 95% when it is not metasomatic alteration. The original rock should belong to Dunite according to the principle of classification and naming of ultramafic rocks of the igneous rock classification and naming scheme. The content of altered minerals in serpentine in rocks is about 50%. Therefore, this jade material should be named serpentine Dunite.

A Dunite address feature in Sichuan and Yunnan region, China:
The ultrabasic rock mass in Sichuan and Yunnan area is the freshest Dunite based ultrabasic rock mass. Its cause of origin is a very important issue. According to its regional geological characteristics and some petrological and mineralogical characteristics, it is believed that it probably came from the [3] of the transitional zone at the bottom of the ophiolite magma chamber.
(1)the main rock types of the rock mass are Dunite, including peridotite and peridotite, and a small number of olivine gabbro. It is a set of transitional rocks composed mainly of ultramafic rocks.
(2)the stratiform structure of rocks, especially in the interior of Dunite, forms a number of rhythmic layered structures. In the edge of the rock mass, the single cycle rhythm of the peridotite of long peridotite in Dunite is also appeared in turn.
(3)the main rock forming minerals are olivine, followed by a small amount of pyroxene, plagioclase and some chromium spinel. Because of the fresh rock, we can see the structural features of the typical upper mantle rock structure, such as the clear twist belt, the broken spot, the megakite, the mosaic structure and the plate like structure. From this point of view, it shows that they are at least close to the special stage of slow environment.
(4)the SiO2 content of all kinds of rocks in rock mass is less than 40%, the content of MgO is between 31.38-47.26, TFeO is 10.77-13.62%, and obviously belongs to ultramafic rock. In figure NiO-Cr2O3 Perth Marr, they belong to the alpine type of rock.
(5)the composition of forsterite in Dunite is Fo 86.3, 88.5, which is very similar to olivine in the cumulate rocks of Newfoundland Bay ophiolite.
(6)as for Dunite, alpine rocks contain two kinds of Dunite. One is the isomer of ophiolite deformed peridotite, the other is the accumulation of Dunite at the bottom of ophiolite accumulative rocks. After comparison, the Dunite in this area should belong to the latter.
(7) the area data indicate that the rock mass in this area is Hercynian. There are dark purple conglomerates overlying the northern and eastern parts of the ultrabasic rock body. Dunite is the main composition of gravel, followed by purple volcanic rocks, gray siltstone and quartz sandstone. The gravel composition is round, different in size and with the characteristics of the breccia. The above features can be completely compared with the six groups of the Upper Sinian series, which means that the ultrabasic rocks may be the remnants of the oceanic crust in Jinning. From the regional perspective, the ultrabasic rocks are distributed on the periphery of the Yanbian group and Proterozoic metamorphosed basalt with deep sea sediments. Therefore, they may be members of the Jinning period ophiolite family. Of course, this is just a question type speculation, which needs a lot of work to verify.