沉积岩中镁钠闪石石棉矿物的初步研究

MAGNESIAN RIEBECKITE ASBESTUS FROM SEDIMENTARY ROCKS——A PRELIMINARY STUDY

Alkali amphibole asbestus is widely distributed in a Mesozoic terrestrial redbed.Preliminary mineralogical study shows that it belongs to magnesian riebeckite asbestus. The mineral contains higher Na, Mg and Fe^3+, lower Al, and is well comparable with that of typical magnesian riebeckite asbestus in chemical composition. A comparasion between the methods used for calculating the crystallochemical formula of amphibole indicatesthat the structural characteristics of amphibole can be best brought out if a total catian number of 15, i.e., x+y+z=15, is taken as the factor for magnesian riebeckite. The infrared spectra for fibrous magnesian riebeckite exhibit two definite absorption bands. The firat one is at 850--1250 cm^-1, involving several minor bands due to the valency vibration of Si--O, with maximum values of 975,1025, 1080cm^-1 respectively. The second absorption band which is attributable to the distortional vibration of Si--O--Si, is detected at 350--600cm^-1, with a maximum value of 440cm^-2. Optically, its refractien iadices bacrease with increasing transition elements, especiany the ratio of Mg/Mg + Fe^2+ +Fe^3+ + Mn. A distinct exothermic effect is observed between 350--400℃, indicating the oxidation of Fe^3+ to Fe^3+. A deep endothermic valley between 970--1020℃ can be attributed to the melting of magnesian riebeckite and the formation of new minerals. The auther oonsideres that fibrous magnesian riebeckite is crystallized in favorable accumulation strata from a Na-, Mg-, Fe-rich silicate colloidal solution that has been derived from country rocks by some alkline ground water duringg the process of sedimentation and diagenesis in terrestrial saline carbonate muds. Magnesian riebeckite formed at terrestrial carbonate saline formations promises to be a potentially important genesis type for alkali amphiboles.

Alkali amphibole asbestus is widely distributed in a Mesozoic terrestrial redbed. Preliminary mineralogical study shows that it belongs to magnesian riebeckite asbestus.The mineral contains higher Na, Mg and Fe3+, lower Al, and is well comparable with that of typical magnesian riebeckite asbestus in chemical composition. A com-parasion between the methods used for calculating the crystallochemical formula of amphibole indicatesthat the structural characteristics of amphibole can be best brought out if a total cation number of 15, i.e., x + y + z = 15, is taken as the factor for magnesian riebeckite. The infrared spectra for fibrous magnesian riebeckite exhibit two definite absorption bands. The first one is at 850-1250cm-1, involving several minor bands due to the valency vibration of Si-0, with maximum values of 975, 1025, 1080cm-1 respectively. The second absorption band which is attributable to the distortional vibration of Si-O-Si, is detected at 350-600 cm-1, with a maximum value of 440 cm-1. Optically, its refraction indices increase with increasing transition elements, especially the ratio of Mg/Mg + Fe2+ +Fe3+ + Mn. A distinct exothermic effect is observed between 350-400℃, indicating the oxidation of Fe2+ to Fe3+. A deep endothermic valley between 970-1020℃ can be attributed to the melting of magnesian riebeckite and the formation of new minerals.The auther consideres that fibrous magnesian riebeckite is crystallized in favorable accumulation strata from a Na-, Mg-, Fe-rich silicate colloidal solution that has been derived from country rocks by some alkline ground water during the process of sedimentation and diagenesis in terrestrial saline carbonate muds. Magnesian riebeckite formed at terrestrial carbonate saline formations promises to be a potentially important genesis type for alkali amphiboles.