Jewelry Lovers

As a token of gratitude for the assistance in arms and the victory won near Najera (i 367), he gave the precious stone to the Black Prince. After the Prince’s death the coveted gem was inherited by the tragic Richard II, and doubtless fell into Bolingbroke’s possession when he ascended the throne as Henry IV: the lovely stone is heard of again at the Battle of Agincourt, where King Henry V wore it in his golden helmet. In Cromwell’s inventory of the Crown Jewels it is described as a “large balas ruby” and assigned a value of a whole 4 pounds! Today this magnificent ruby-red spinel, set in a Maltese cross of brilliant-cut diamonds, surmounts the Imperial State Crown, and year by year is admired by thousands in the Tower of London. The stone most probably came from Burma; it has never been cut and was nearly 5 centimeters across when last measured. The largest spinel known hitherto, a waterworn crystal of 520 carats, is in the Mineral Department of the British Museum (Natural History), together with a well-formed octahedron of 355 carats; a third giant, of nearly 400 carats, lies in the Diamond Treasury in Moscow.

Nature has endowed every gemstone with characteristics of the most individual kind. In addition to its high aesthetic value, especially its vibrant colors and striking clarity, spinel has still other enhancing qualities, such as its excellent “cuttability” and its capacity to withstand great heat without change. For all this wealth of virtues, it is a most regrettable fact that spinel is at present not accorded its due recognition; for the fine red and blue spinels, though they are poor relations of ruby and sapphire, nevertheless occupy a distinguished rank among gemstones.

The gay variety of colors results from its cheerful willingness to exchange hereditary components for foreign coloring elements. Thus small quantities of chromium, in the order of about i to 2 percent, may displace aluminium and in this way give rise to the red hue. Red spinel is in fact the only gemstone which can even approximately rival the red ruby. With unexpected diversity it spans all degrees of the red scale and even glows in blood red, brick red, as well as rose-red guise, to which the bright orange-colored fire spine! is added as a pretty variant. In wonderful color gradations the purple spinel shades over into blue-green and ink-tinted nuances of the blue varieties, of which the extremely rare pure deep blue rates the highest value. Iron, titanium, or zinc (gahnite) are responsible for these shades of color when they displace small percentages of magnesium in the spinel composition.

Violet spinels are common; distinctly green ones, in which iron replaces a little aluminium, are virtually unknown, and yellow ones do not occur. What spinel lacks in the color saturation of ruby and sapphire, it makes up by dint of its clear transparency and its brilliance, often enhanced by flawless purity. But this does not mean that all spinels are blessed with absolute purity; on the contrary, in many spinels characteristic inclusions occur as welcome identification marks. Indeed, even in this sphere the spinel seeks to rival corundum, in that occasionally its body is interspersed by a fine silky network of needles of rutile or sphene, whence an alternating play of four- and six-rayed stars is induced upon its convex surface.

Spinel is a combination of magnesia (MgO) and alumina (Al₂0₃) and thus a magnesium aluminate, It crystallizes in sharply defined octahedra. It often shares with corundum the same places of origin, mainly in Burma where it is universally accompanied by ruby, and in Thailand, where it is regarded as a “pilot mineral” of corundum. Further important spinel deposits exist in Ceylon.

Both spinel and corundum originate from the same pegmatitic-pneumatolytic contact metamorphism. Spinel was, as it were, the herald of the subsequent ruby, crystallizing out in the generation before ruby, in fact, so long as the magnesium dissolved out of the dolomitic limestone was still available. Because of this—in the course of the crystallization processes in which the several mineral generations were involved, magnesia and alumina were continuously consumed—the magnesia was finally used up in the spinel, and only very little alumina was left. This is one explanation why, for example, near Mogok about five times more spinels are found than rubies, and why ruby becomes so extremely rare because the raw material has been exhausted in the spinel. But the image of spinel as the herald of corundum survives even in our day, for it is willingly purchased by every gem fancier who cannot or not yet afford a ruby or a sapphire. The lovely colors of spinels and their strong brilliance will always gladden the heart of a gemstone lover.

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