Study On The Gem Mineralogical Characteristics Of Apatite From Three Producing Areas

Apatite is a kind of gem mineral that is relatively widely distributed in the lithosphere and produced in many regions of the world.There are many sources of apatite,but the information on the source is not yet clear.Among the many producing areas of apatite,Mexico,Madagascar and Morocco are three very important producing areas.In this paper,the gem mineralogy and chemical elements of apatite from Mexico,Madagascar,and Morocco are studied.Gem microscopes are used to observe the inner inclusions of apatite from different places.Raman spectrometer and infrared spectrometer are used to explore the spectral differences of apatite in different origins and different crystal directions;using electron probes to determine the major elements of apatite in the three origins;using LA-ICP-MS to explore the indications of trace elements in Mexican apatite.The types of characteristic peaks in the Raman and infrared spectra of apatite from the three origins are almost the same,and the main characteristic peaks are all caused by the vibration of [PO₄]^3-.However,when different crystal directions are selected for testing,the position and number of characteristic peaks will change.The test results of the electron probe show that both Ca O and P2O5 are the main components of apatite,with little change in the three producing areas.The content of Ca O is between53.6⁵5.22wt% and the content of P2O5 is between 39.06⁴1.38wt%.The apatite from the three producing areas all showed the characteristics of rich in F and poor in Cl,and was identified as fluorapatite.There are no significant differences in Raman spectra of apatite from the three origins,but there are regional differences in basic gemological characteristics,infrared spectral characteristics and major element characteristics.The difference in basic gemological characteristics is reflected in: Mexican apatite contains a large number of parallel C-axis tubular inclusions and has a higher relative density than other apatites(3.21);under short-wave ultraviolet light,Madagascar apatite fluorescence relatively strongest,it is a medium blue-violet fluorescence.The difference in infrared spectra is reflected in: Mexican apatite OH-stretching vibration peak VOH is located at 3482cm^-1and 3538cm^-1,Madagascar apatite OH-stretching vibration peak VOH is located at3556cm^-1,and Moroccan apatite OH-stretching vibration peak VOH is not seen;the V3-V4 difference frequency band of [PO₄]^3-is not seen in Mexican apatite and Madagascar apatite,the V3-V4 difference frequency band of [PO₄]^3-is seen in apatite from Morocco,located at 470cm^-1.The difference of major elements is reflected in: Mexican apatite has a lower SiO₂ content and a higher Na₂O content;Madagascar apatite has a very high F/Cl value and a lower Cl content;Moroccan apatite has Very low F/Cl value.The test results of LA-ICP-MS show that the rare earth elements in apatite in Mexico generally show a "right-leaning" distribution pattern,showing the characteristics of light rare earth enrichment and heavy rare earth loss.The negative Eu is abnormally significant,and the magma is in a medium reduction state.