PEARLS 591 



Dull white pearls, in which the beautiful lustre of typical pearls is absent, are probably 

 produced by all molluscs, the shells of which have a white inner surface. Such pearls are 

 found in the pilgrim-shell {Pecten jacobceus), the giant-clam {Tridacna gigas), in many 

 varieties of the common fresh- water mussels {Unio and Anodonta), in the razor-shell 

 {Solen), and many others. Dull white peaiis have indeed been found in the edible oyster 

 {Ostrea edulis) in spite of the absence of mother-of-pearl in its shell ; and it has been 

 related by a dredger how he found a pearl in an oyster he was eating, and obtained for it 

 22 thaler (66s.). The occurrence of pearls in certain univalves has been mentioned 

 already. The large West Indian Strombiis gigas, and the East Indian Turbinella 

 scolymus yield very beautiful rose-red pearls, in which, it is true, there is no mother-of- 

 pearl layer, and which, therefore, are not true pearls. They are distinguished from the 

 latter by the fact that their colour, like that of the univalve shells in which they originate, 

 gradually fades away with the lapse of time. 



Some pearls exhibit the colour-eiFects characteristic of mother-of-pearl, but only to a 

 slight degree and of very pale bluish, greyish, and reddish shades. In such pearls the outer 

 layer of mother-of-pearl substance is not continuous over the whole surface, but is confined 

 to small, irregularly bounded areas separated by areas from which it is absent. In addition 

 to the elevations and depressions usually present on the surface of a pearl, there are also 

 delicate and irregularly curved grooves, which pursue either approximately parallel courses 

 or form closed curves of irregular form. The colours exhibited by such pearls are due, as 

 in mother-of-pearl, to physical causes connected with the structural peculiarities of the 

 surface. 



The value of a pearl, and the uses to which it is applied, are considerably influenced by 

 its form, and in this respect there is a certain amount of variety among pearls. They 

 may be perfectly spherical, more or less ovoid, or pear-shaped. Pear-shaped and elongated 

 ovoidal pearls are referred to as pear-pearls, and the former more especially as bell-pearls, 

 while spherical pearls are known as pearl-drops or pearl-eyes. Ovoidal pearls sometimes 

 contain two nuclei, each of which is invested by its own series of concentric coats, only the 

 outermost coats of the pearl enclosing both nuclei. We have evidently, in such cases, two 

 originally separate pearls which have become enclosed in a common coat, and thus formed 

 a single ovoidal pearl. 



Pearls of very irregular form are known as baroque pearls (" barrok pearls "), and are 

 specially abundant in the fresh-water pearl-mussel. These also are used as ornaments and 

 for other purposes, but are less valuable than those of a more regular form. As extreme 

 examples of irregularity in form may be mentioned two pearls described by the Parisian 

 jeweller Caire, one of which resembles in form the head of a dog, and the other the Order of 

 the Holy Ghost. 



The size of pearls is very variable. One of the largest known is the property of the 

 Shah of Persia ; it is pear-shaped in form, and is 35 millimetres long and 25 thick. 

 A still larger one formed part of the famous collection of pearls and precious stones 

 of Henry Philip Hope, and is figured and described by B. Hertz in his catalogue (London, 

 1839) of this collection. This pearl weighs 3 ounces (troy), or about 454 carats ; it is 

 irregularly pear-shaped in form, measuring 2 inches in length, 4| inches in circumference at 

 its thicker end, and 3^ inches at its narrower end, and is thus almost as large as a hen's 

 egg. For a length of about \l inches this gigantic pearl is of a fine bright "orient," the 

 remainder being of a fine bronze tint or dark green shaded with copper colour. A portion 

 of the shell on which it grew is left adhering to it, but this of so fine an " orient ■" and so 

 well polished that it is scarcely recognisable as such. In the Austrian Emperor's crown 



