The Feature and Origin of Chrysanthemum Stone of Hubei

Chrysanthemum stone is a kind of viewing stone what distinct from all other, mostly refer to a white rock likes the petal on the black and gray bottom, it is carbonatite by sedimentary origin. This kind of stone is a natural, clear distinction of white and black, a thousand fantastic flower are composed of the white rock, as if the white chrysanthemums are in full flower, are a feast for the eyes, and it has a fine texture, neither too hard nor too soft, easy to carve as various arts and crafts stone to view, noble and elegant on it, it is rare collection by people like.

The resources of chrysanthemum stones are limited, they were discovered only in Hubei province, Hunan province, Shangxi province and Jiangxi province in China, up to now, no find it overseas.

Chrysanthemum stone was first discovered in Yonghe town, Liuyang county of Hunan province in China, was former more 200 years. Hubei chrysanthemum stone is indigenous to Enshi of Hubei province, is known as the three gorges chrysanthemum stone, they are first discovered in Xuanen county of Hubei province in 1987, after it, people found chrysanthemum stones in other cities of Enshi county. Chrysanthemum stone is widely distributed and very large over Hubei province, being an important producing area in China.

People discovered chrysanthemum stones to several hundred years ago, they are made into various viewing stones and crafts to go round. It is an exotic flower of the jade arts. In order to better understand the character of Hubei chrysanthemum stone, based on investigation of field geology to get the sample was going to thin section identification indoor, x-rays diffraction analysis and chemical analysis etc, to summarize the origin of Chrysanthemum stone from the angle of petrology.

1. The origin of geology

We knew, Hubei chrysanthemum stone is distributed in Enshi, Xuanen, Jianshi of Hubei province, etc. This geotectonic area is situated Yangzi earth's crust, from Sinian to Triassic Epoch, it is still on a settling process, has deposited 10000 meters thick stratum predominate in carbonatite. Hubei chrysanthemum stone beds occur in the member of Lower Permian Qixia Formation 200 million years ago, it is in the same layer with Hunan chrysanthemum stone.

Lower Permian Qixia Formation in Enshi area divided into two lithological members from up to down, the lowercoaly clastic rock, is known as horse shoes member. The upper is composed of carbonate rock, is called limestone member. The limestone member is in a steady position of the lithology and thickness of Enshi region, the thickness is 139.22~272.65 meter, to divide into two members under lithological, the upper is chert limestone concretions, the lower is bioclastic limestone and calcarenite. Chrysanthemum stones mostly are produces in bioclastic limestone and calcarenite, and have no chrysanthemum stones in other this of rock.

Analysis From structural condition, usually Hubei chrysanthemum stones are situated the flank of opening and syncline, Triassic system strata in the core stratum. For example Enshi chrysanthemum stone is situated the flank of Huaping county, the axial warp is NE45° of the syncline, the core stratum is close the aclinic aspect, inclinationangle is around 15°, the inclination angle situated in the strata of Permian age of two sides is 25°~45°.

Based on observations, Hubei chrysanthemum stone present in zonal distribution along valley, forming a zone, it is 30~40 kilometers. In this zone, chrysanthemum stone is discontinuous distributed, some sections they are gathered, there are dozens of chrysanthemum stone in one square meter, another sections they was divided, one to two chrysanthemum stones in several of square meters irregularly.

2. The character of the rock

Hubei chrysanthemum stone in shape presents block, dense and hard, it is composed of both grey-and-black fundus and white chrysanthemum shape, sometimes we could also see the white calcspar through huger organism fossils to form the flower. The fundus of chrysanthemum stone is grey-and-black, consist of biology debris and micrite. Biology is abundant in variety, the kind of fusulinids, brachiopods, foraminifera, bryozoan, etc. The debris is vary in size from 0.1mm to 2mm, some of these relatively large, about 20cm. the micrite is slender granule or tabular granule, particle size from 0.005mm to 0.03mm, as a binder between the grabule of biology debris. The mineral in fundus mainly consist of calcite, second a little quartz and dolomite, trace minim mineral consist of carbon material, pyrite, limonite, etc, sometimes we could see albite crystal and clay mineral hydromica etc. The chemical constituents of fundus mainly is CaO and CO.. 2.., next SiO.. 2.. and MgO, and other elements is extremely rare, it squares with mineral.

The flower of chrysanthemum stone is white, the fundus is grey-white, depending on shape integrated degrees to divide into three sorts, first there are petals and buds, is a top-grade, the radial petal opens around are very complicated, likes butterfly or silk ball or phoenix tail etc. the bud is roundness, in the center of the petal. Chrysanthemum stone size is different, general diameter from 5cm to 15cm, the largest from 40cm to 50 cm. Second no bud in the petal, although this is also beautiful but it is not the best beautiful than these flower with bud, the same character on it. Third no shape of flower in chrysanthemum stone, it is bottom-grade in chrysanthemum stones, it likes mountains with irregular shape, likes star drop on the fundus.

The radial petal of chrysanthemum stone is one pieces close or fitful rhombi crystal, its mineral element mainly are calcite and chalcedony(quartz), some of them contained strontianite and lazuli. The order in which mineral is generated and phenomena is expressed clearly, we found there are biology calcarenites are replaced from the microscope. along lazuli edge. Strontianite in the center, surrounding calcites, chalcedony (quartz), and so on. The elements in bud are mainly consisted calcite and chalcedony (quartz).Chemical Compositions of chrysanthemum stone consists chiefly of CaO, CO.. 2 and SiO.. 2,some of them include SrO, and SrO contents against with CaO, SiO.. 2.., mean if CaO, SiO.. 2, contents more highly, SrO is more less, they will occur strong with their interaction, the early in which strontium mineral is greatly replaced. Besides, the high content and less fundus is the character of chrysanthemum stone when the elements chrysanthemum stone than the fundus.

3. Discussion on the formation

About the origin of chrysanthemum stone, at present has been disputing, never see eye to eye on anything. Some believe that it is formed by contact each other, another think that it is an ancient living creature fossil, and so on. Now no any reliable evidence to report for these words.

According to the survey on geological environment and rock character of Hubei chrysanthemum stone, the chrysanthemum stone has much strontium, carbonate rock interact to form crystal in the late rock-forming is deeply buried. We will make a brief on material source, generation phase, generation type etc.

On material source, as a depositional carbonate rock, chrysanthemum stone only occur in the bioclastic lime stone of the lower Permian Qixia Formation, no be discovered in other rocks. So the material source of chrysanthemum stone necessarily relate to bioclastic limestone. Knew it from chemical composition, they have the same chemical element, rich in Ca, Si and CO.. 2, etc.

Where is Sr as one of the most element in chrysanthemum stone? Analysis on Sr element of the Permian Qixia Formation, the content of Sr of bioclastic limestone in Enshi chrysanthemum stone is maximum, about 0.085% ~ 0.135%, belong to strontium high limestone. The lower Sr limestone in Ezhou of Hubei province, no include chrysanthemum stone. It is therefore not difficult to see, the Permian in Enshi area is bioclastic limestone of high strontium, not only provided the basis element of chrysanthemum stone, and provided material source for strontium mineral. Anyway can't occur chrysanthemum stone if no carbonate rock of high strontium, the reason what chrysanthemum stone is rare and is formed in a grade.

The generation phase.

Enshi chrysanthemum stone is formed in Lower Permian Qixia Formation, was formed two hundred million years ago. More evidence showed, different environments and different diagenetic stage formed bioclastic limestone in fundus and chrysanthemum stone. From loose sediment to solid diagenetic in formed bioclastic limestone, diagenesis have the Characteristicof gravity gum, the pressure solution sutures, crystallization, dolomitization and authigenetic feldspar, reflecting it saw diagenetic stage in early and middle. Chrysanthemum stone mineral is made up of coarse crystalline texture and replacement texture, include fundus rock in the granule of chrysanthemum stone, to result chrysanthemum stone formed after the fundus rock is coagulated. Moreover, thin vein in calcite later mixed some chrysanthemum stones, or connect with it. So chrysanthemum stone is formed in the later deep-buried stage in the middle of diagenesis.

The formation way.

In the whole Enshi Area mostly is sedimentary rock strata, no any Igneous activity and metamorphism. Therefore chrysanthemum stone formed relate to sedimentary rock diagenesis, formation process from biociastic limestone to deep-buried stage later. Due to high temperaturepressure, there are many Sr, Ca, Si, CO.. 2, ect in granule, probably the reason of the factor of evaporation and specific gravity etc, made enough Sr and 2, formed Celestine stone with SO.. 3 and 2, grown into coarse crystalline, a whole crystallineform. After it, with the change of the composition, early formed minerals were transited to later minerals, generate strontianite to celestite, chalcedony(quartz), and calcspar to celestite, strontianite, and so on, better replacing or complete replacing, only reserved a gloss on rhombohedron. As mentioned above, Hubei chrysanthemum stone is formed through recrystallization to metasomatism.