Comparison On Common Species Of Laosstone And Similar Shoushan Stone

Laos Stone has entered Chinese seal stone market since 2013 and caused a great impact.Laos Stone has a huge production,excellent stone quality and are similar to Shoushan Stone,one of the four major precious seal stones in China.This not only confuses consumers,but also causes a certain impact on the stable development for the seal stone market.Therefore,it is necessary to conduct systematical research on common Laos Stone varieties and compare them with the corresponding Shoushan Stone varieties.It has a great significance for scientific identification of the origin.This paper tested Laos Northern Yellow Stone,Laos Peachblossom Stone and Laos“Ducheng”for their gemological and mineralogical characteristics with the help of various experiment methods,then compared which to that of similar varieties in Shoushan Stone?Tianhuang,Gaoshan Peachblossom Stone and Ducheng Pit Stone?in order to find differences and provide a reference for the origin identification.According to macroscopic observation and gem microscope observation,common Laos Stone varieties and similar Shoushan Stones have slight differences in their appearance characteristics:1)Laos Northern Yellow Stone usually have uneven color distribution.Laos Northern Yellow Stone usually has no layer of rough stone skin but always contains pink lumpy mineral inclusions and black punctiform mineral inclusions.Tianhuang's color is relatively well distributed.The interior of Tianhuang is relatively pure.Impurity minerals are rare in Tianhuang,but turnip grains and red cracks frequently appear.2)"Peach blossom"inclusions in Laos Peachblossom Stone always formed in cluster shape and mostly spread in white and white transparent substrates while"peach blossom"inclusions in Gaoshan Peachblossom Stone are spot-like and generally arrange separately in the reddish transparent substrate.The distribution of"peach blossom"inclusions in Laos Peachblossom Stone is denser than that of Gaoshan Peachblossom Stone.3)The“waterline”of Laos“Ducheng”are thinner and has more layers than that of Ducheng Stone,while Ducheng Pit Stone's“waterline”is thick.According to the results of X-ray powder diffraction test,Laos Northern YellowStone usually compose with pure dickites,which are disordered dickites.Tianhuang have three types:dickitic type,nacritic type and illitic type.The main mineral composition of Laos Peachblossom Stone is dickite and transition minerals of dickite and kaolinite,also contains a few quatity of quartz.The main constituent minerals of Laos“Ducheng”is dickite with good crystallinity and dickite-kaolinite transition minerals with high to low degree of crystallization.The main constituent minerals of Ducheng Pit Stone includes dickite with ordinary crystallinity and dickite-kaolinite transition minerals with low degree of crystallization.The FTIR spectra show that:the main constituent minerals of Laos Northern Yellow Stone are disordered dickite.White transparency part and the flocculated"waterline"part contain more ordered dickite,which is in the form of disordered dickite to ordered dickite.The mineral composition of Laos Peachblossom Stone are disordered dickite to kaolinite,while the mineral composition of Gaoshan Peachblossom Stone compose with ordered dickite.The Raman spectroscopy test results show that impurity minerals contained in the Laos Northern Yellow Stone include barite,anatase,diaspore and hematite.Both of the"Peach Blossom"inclusions in Laos Peachblossom Stone and Gaoshan Peachblossom Stone are hematite.Moreover,Gaoshan Peachblossom Stone also contains anatase.Laos“Ducheng”contain hematite and anatase as impurity minerals.In addition to hematite,Ducheng Pit Stone also contain pyrite and diaspore.SEM observations show that,1)Turnip vein in Laos Northern Yellow Stone are finely dispersed and difficult to observe by naked eyes.The turnip vein is mainly in the form of dendritic and short veins in the substrate of Laos Northern Yellow Stone.Strip-like,flocculent and vein-like turnip veins densely distributed in the substrate of Tianhuang.2)The particles in Laos Peachblossom Stone closely arrange in a semi-self-shaped flaky shape,and the edges of the particles are irregular and sharp.3)In Laos“Ducheng”stone,the mineral particles in the transparent layers of“waterline”have clear orientation,all of which are closepacking flaky particles arranged in the direction parallel to the“waterline”.Densely distributed dickite granules and the vein-like svanbergite compose the other layers of“waterline”in Laos“Ducheng”Stone.The finer silky svanbergite mixed between dickite particles compose the“waterline”in Ducheng Pit Stone.There are dickite particles arranged in block mass within the“waterline”in Ducheng Pit Stone.The dickite particles are in a layered structure parallel to each other within the block mass mentioned before.EPMA test and whole-iron chemical analysis indicate that Fe³⁺causes yellow of Laos Northern Yellow Stone.The iron ion content shows a trend from high to low as the color changed from deep to light.The red color of Laos Peachblossom Stone come from the densely distributed red microcrystalline hematite.LA-ICP-MS test reveal the trace elements characteristics of common Laos stone varieties and similar Shoushan stone varieties.According to the content plots of Ga-Sr,Cr-Rb and Ga-Rb,it is easy to tell the difference between Laos Northern Yellow Stone and Tianhuang;Ga-Sr and Rb-Ba element content plots can help to distinguish the Laos Peachblossom Stone and Gaoshan Peachblossom Stone basicaly;Ni-Cr element content plot could help to distinguish Laos“Ducheng”and Ducheng Pit Stone.However,most of these plots have overlaps between two species and make it hard to distinguish them precisely.Discriminant analysis and stepwise discriminant method can effectively distinguish three groups of similar species in Laos and China.The correct rates of verification of unknown samples by three groups of discriminant functions were 92.9%,97.2%and 88.9%,respectively.The accuracy rate of corresponding stepwise discriminant model is up to 100%and the reliability of the model is high.There are also differences in the characteristics of rare earth elements between common Laos Stone varieties and similar Shoushan Stone varieties.The REE partition pattern diagrams of Laos Northern Yellow Stone are flat and right tilting while that of Tianhuang are right tilting.The REE partition pattern diagrams of Laos Peachblossom Stone and Gaoshan Peachblossom Stone as well as Laos“Ducheng”and Ducheng Pit Stone are in the type of right tilting.According to the discussions in this paper,the ore-forming temperature of impurity minerals in Laos Northern Yellow Stone is relatively high and is usually formed first in reduction environment,while the dickite in Laos Northern Yellow Stone is formed in shallow surface oxidation environment.Losing absorbed water makes the substrate part of Laos Peachblossom Stone pale,which weaken the visual contrast between substrate part and red“peachbolossom”inclusions.This might be the reason for the color fading of Laos Peachblossom Stone.The cause of the“water line”in Laos“Ducheng”Stone may relate to the multi-phase activities of ore-forming fluids and the differences in mineral composition.The cause of the“water line”in Ducheng Pit Stone may relate to the different-period crystallization of ore-forming fluids and the differences in mineral composition.In summary,comprehensive using the method and analysis mentioned above would help distinguish Laos Seal Stone and Shoushan Stone.This conclusion and the identification method of origin have certain reference significance for the identification between other varieties in Shoushan Stone and Laos Seal Stone as well as the identification of seal stones from different places of origin.