282 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 13 
MINERALOGY.—Methods for distinguishing natural from cultivated 
pearls! F. E. Wricut, Geophysical Laboratory. 
Efforts have been made for several centuries to induce pearl-growing 
oysters and mussels to produce pearls comparable in quality and size 
to the “‘natural” or ‘‘ normal’ pearls found by pear! divers in different 
parts of the world and known tothe trade as fine pearls. It is a simple 
matter to provoke formation of “‘blisters’’ and baroque pearls, but only 
recently has a Japanese, Dr. K. Mikimoto, succeeded in developing a 
suitable method for inducing pearl oysters to grow pearls which are 
spherical in shape and similar in external appearance to fine pearls. 
His process, which has been patented, is essentially the following: 
A pearl oyster is first removed from its shell; from its outer, shell- 
secreting mantle, a patch is dissected off, large enough to enclose, as a 
sac tied at the neck, a foreign nucleus, such as a bead of mother-of-pearl 
or even an inferior pearl. Each bead thus enveloped by the shell- 
secreting epidermis is embedded in the sub-epidermal tissues of another 
live oyster, which, after proper treatment of the wound, is returned 
to its native habitat where in the course of a few years a coating of 
pearl around the inserted bead may be deposited. The success of this 
process is due, as was first emphasized by Dr. H. Lyster Jameson,? to 
the “presence, in the sub-epidermal tissues of the oyster, of a closed 
sac of the shell-secreting epidermis and not to the presence of an irri- 
tating foreign body” as has been often supposed. 
The pearls thus induced by the Mikimoto process are now on the 
market and pearl merchants have had difficulty in distinguishing 
natural Japanese pearls from the cultivated pearls of Mikimoto. 
A short time ago the writer’s interest in this problem was aroused by 
Dr. G. F. Kunz of New York who kindly loaned him, for examination 
and comparison, examples of the Japanese cultivated pearls and of 
fine pearls. In the Japanese pearls the centers were without exception 
mother-of-pearl beads, and the methods described below are based 
in large part on the ability of the observer to recognize the mother- 
of-pearl nucleus. 
Mother-of-pearl or nacre substance is composed of alternate laminae 
or layers of calcium carbonate and of a horny organic substance called 
conchiolin. In most of the mother-of-pearl shells examined by the 
writer the carbonate is the mineral aragonite in the form of needles 
elongated parallel with the acute bisectrix and oriented perpendicular 
! Received June 19, 1923. 
2 Proc. Zool. Soc., I, 140-166. 1902; Nature, Jan. 22, 1903, p. 280; Nature, May 26, 
1921, p. 397. . 
