gems, garnet, pyrope-almandine, rhodolite, Macon County, North Carolina, North America

It is well known that a whole series of garnets exists from pyrope to almandine, due to the isomorphous replacement of Fe for Mg in the basic chemical composition, and for those lying near the middle of the series Anderson has proposed the name “pyrandine”. It is not so well known that a distinct subvariety of the series is recognized which, because of its rose-red to pale violet colour, has been named “rhodolite” (Gr. rhodon, a rose). It is a rare stone and many gemmologists may not have encountered a specimen. According to Phillips, this variety was found, in limited quantity, in Cowee Valley, Macon County, North Carolina. However, a few other sources are known and Sinkankas reports that fine quality material of unprecedented size has recently appeared from Tanzania. Very occasionally, stones having the colour described for rhodolite are encountered, but carrying no qualification other than “garnet”. It seems that there is some reluctance to apply the term “rhodolite” unless it is known that the stone originated from Macon County. If, however, a garnet possesses physical features, in addition to colour, which mark it as a distinctive entity within the pyrope-almandine series, it seems only reasonable that it be granted its status and accorded its value, irrespective of its source. Rhodolite is a subvariety near to pyrope and Webster notes that its composition lies between pyrope and almandine in the ratio of 2:1. The constants for pyrope show a considerable range and the figures given by different authors do not exactly correspond, particularly in the upper limits. This is not surprising, since one is reaching the intermediate (“pyrandine”) type. Phillips states the R.I. range to be from 1.730 to 1.751, but Anderson gives 1.76 as the upper limit and Webster records 1.77. It is perhaps rather curious that the R.I. of rhodolite, which belongs to this series, has only the single figure of 1.76 recorded against it. The same applies to the S.G.; Phillips gives a range of 3.65 to 3.82 for pyrope and other authors quote similarly, yet the single figure of 3.84 is given for rhodolite. Apart from these two constants, the only definite information recorded in standard works is that rhodolite shows the absorption bands characteristic of the almandine spectrum.