Magnetic susceptibility, a better approach to defining garnets

Abstract

Using a new, non-destructive method of gem testing, magnetic susceptibility, the authors show how the major endmember composition of any garnet may be confi dently predicted by plotting RI against measured susceptibility. On this diagram, eight end-member garnets are plotted, so that any measured garnet can be placed in an appropriate ternary area. This method shows how previous methods of identifying garnetsby their colour, RI and spectrumare insuffi cient to accurately identify chemistry in the garnet group. Furthermore, it can be done with inexpensive equipment available to most gemmologists.

Structural and Microstructural Correlations of Physical Properties in Natural Almandine-Pyrope Solid Solution: Al70Py29

“…22 The weight percentage of oxides of various elements detected from EPMA and mol.% of different garnets in the solid solution are given in Table I The electron microprobe results gives the proportion of various types of garnets present in the mineral, and it is deduced to be 70.05 mol.% of almandine and 28.56 mol.% of pyrope. Hence, the present mineral can be labeled as Al 70 Py 29 . Other garnets present are below 2 mol.% and can be considered as impurities.…”

“…27 Measurement of such physical properties of garnets is a suitable method to identify their chemical composition. 28,29 Usually ternary diagrams or triangular plots are used to predict the chemical compositions of solid solutions using the physical properties. 29,30 Here, an alternative method is used to relate the magnetic properties and chemical composition of almandine-pyrope solid 31 Thus, magnetic measurements can indicate the quantity of these elements in the solid solutions.…”

“…28,29 Usually ternary diagrams or triangular plots are used to predict the chemical compositions of solid solutions using the physical properties. 29,30 Here, an alternative method is used to relate the magnetic properties and chemical composition of almandine-pyrope solid 31 Thus, magnetic measurements can indicate the quantity of these elements in the solid solutions. The experimental value of effective magnetic moment can be calculated from the Curie's constant, C, using the equation 31 :…”

“…Since the sintering temperature was low, density of the samples obtained was about 67%. Although heating 29 ) possess low dielectric constant (e r ), the values of which ranges from 6 to 7.4. The microstructural analysis shows that the sample is highly porous at these temperatures.…”

“…The densification of Al 70 Py 29 can be improved by hot isostatic pressing and cold sintering, which will be done as a future work. Further, Al 70 Py 29 can be used as a filler for fabricating ceramic polymer composites. Also, the present mineral is cheap and ''green'' as it contains Fe, Al and Si elements only.…”