The Characteristics And Gemological Insignificance Of Rutile Inclusions In Crystal From Brazil

Crystal is one of the varieties of precious gemstones in the world,while the one containing rutile is more valuable.Minas Gerais,Brazil is one of the most important origin of the world,and formation and characteristics of the inner rutile inclusions provide an important basis for the research of crystal containing rutile.In this paper,taking 50 pieces of crystal from Brazil as the research object,rutile inclusions from the crystal were seperated for mineralogical and geochemical analysis,including scanning electron microscopy,X-ray powder diffraction,EMPA chemical composition analysis,and ion probe technology U-Pb dating.Combined with review of crystal inclusions,the following conclusions were obtained.(1)The scanning electron microscope and X-ray powder diffraction experiment confirmed that the gold inclusion was rutile while the black one was hematite.Rutile inclusions could exhibit forms like tree,column or hair and needle.Both the trunk of tree-like rutile and needle-like rutile has the same axis of [001],which may be linked with the crystallization of cooling rate.(2)On the perpendicular to the C axis,rutile mostly exists bamboo-like fracture.The bonds perpendicular to the C axis are stronger than the bonds parallel to the C axis,which leads bonds parallel to the C axis are more susceptible to the influence of the temperature,and causes the rutile fracture,which has the important significance for the identification of crystal containing rutile.(3)Most of the samples present rutile star at the corner of hematite,and the angle between two rutile bundles is 60°,the main reason is presumably that rutile crystallization is dominated by the trigonal model of hematite.(4)In EMPA chemical composition analysis,using the Zr-in-rutile thermometers,The crystallization temperature of the rutile in Brazil is 431 or 491°C.Cr content<Nb content,which indicate the metapelitic source lithologies.(5)Ion probe technology U-Pb dating yield a U-Pb age of 582 ± 20 Ma.The crystallization temperature of rutile is less than the closure temperature,therefore,rutile U-Pb age represents the crystallization age of rutile and the crystallization age of the main mineral crystal.The study of rutile inclusions has great significance to research the geological age and formation temperature of crystal and for the application of gemstone.