Spinels, when red, are almost always more yellowish or more purplish than fine corundum rubies. They are also singly refracting and hence exhibit no dichroism and therefore lack variety of color as compared with true ruby. Some especially fine ones, however, are of a good enough red to deceive even jewelers of experience, and one in particular that I have in mind has been the rounds of the stores and has never been pronounced a spinel, although several "experts" have insisted that it was a scientific ruby. The use of a dichroscope would have saved them that error, for the stone is singly refracting. Spinels are usually clearer and more transparent than garnets and show their color better at a distance or when in a poor light. Tourmaline of the reddish variety (rubellite) is seldom of a deep red. It is more inclined to be pinkish. The dichroism of tourmaline is stronger than that of ruby and more obvious to the unaided eye. The red of the rubellite should not deceive anyone who has ever seen a fine corundum ruby. YELLOW STONES Considering next the stones of yellow color, we have the following species to deal with: (1) diamond, (2) corundum, (3) precious topaz, (4) quartz, (5) beryl, (6) zircon, (7) tourmaline. YELLOW ZIRCON RESEMBLES YELLOW DIAMOND. Here we have less opportunity to judge of the species by the color than was the case with the red stones. The diamond, of course, is easy to tell, not by the kind of yellow that it displays, for it varies greatly in that respect, but rather by its prismatic play blended with the intrinsic color. Its luster also gives an immediate clue to its identity. It is necessary, however, to be sure that we are not being deceived by a yellow zircon, for the latter has considerable "fire" and a keen luster. Its strong double refraction and its relative softness, as well as its great density will serve to distinguish it. Of the other yellow stones, the true or precious topaz is frequently inclined to a pinkish or wine yellow and many such stones lose all their yellow (retaining their pink) when gently heated. The so-called "pinked" topazes are thus produced. The yellow corundum rarely has a color that is at all distinctive. As far as color goes the material might be yellow quartz, or yellow beryl, or yellow zircon, or yellow tourmaline (Ceylon type). Many of the yellowish tourmalines have a decidedly greenish cast (greenish-yellow chrysoberyl might resemble these also). However, in general if one has a yellow stone to determine it will be safer to make specific gravity or hardness tests, or both, before deciding, rather than to rely upon color. LESSON XII COLOR--_Continued_ GREEN STONES Let us first consider what mineral species are most likely to give us green stones. Omitting the semi-precious opaque or translucent stones we have: 1. Grass-green beryl (the emerald) which is, of course, first in value among the green stones and first in the fine quality of its color.