I have the pleasure of exhibiting to the Academy four diamonds, obtained from separate localities in this State. Three of them are crystals, having the form of an icositetrahedron; the other has been cut, and is set as a ring stone.
The First Specimen—Is from Forest Hill, in El Dorado County. Its weight is 0.369 gramme, or 5.673 grains—equal to rather less than 1½ carats. Its color is good, but it has a small cavity and discoloration on one of the solid angles, and it is less symmetrical than the second specimen. This crystal was found at a great depth from the surface in a tunnel run into the auriferous gravel at Forest Hill. I procured this stone from Mr. Tucker, the well-known jeweler.
The Second Specimen—Is from French Corral, in Nevada County. It weighs 0.3375 grammes, or 5.114 grains—equal to about 1⅓ carats. Its form is symmetrical, color slightly yellowish. Its lustre has been dimmed slightly by having been subjected to a red heat as a test of its authenticity. The auto da fé is hardly the test a chemist would select for pure carbon! It is remarkably destitute of flaws. This crystal was washed out from the cement in the deep gravel washings for gold at French Corral, and was found in the sluice boxes. It belongs to Mr. Egbert Judson, of San Francisco, from whom I derive this information.
The Third Specimen—Is smaller and less perfect than either of the preceding. It was found at Fiddletown, in Amador County. It weighs 0.2345 gramme, or 3.619 grains—a little less than one carat. This crystal is distorted, and has several reëntering angles and cavities. Mr. M. W. Belshaw, to whom it belongs, informs me that since 1855, five diamonds have, to his knowledge, been found at Fiddletown, where he then resided; none of them weighing much over one carat. All these specimens were found in a gray cemented gravel underlying a stratum of “lava” or compact volcanic ashes, and were found in searching for gold.
The Fourth Specimen—Is from Cherokee Flat, in Butte County, and has been cut and set in a ring. Mr. Geo. E. Smith, of 605 Montgomery Street, San Francisco, who is an expert in diamonds and owns the specimen exhibited, informs me that he has seen fifteen crystals from this locality, and has authentic advices of at least forty, all of which have been found in deep gravel washings, and are believed to come from a stratum of about three feet thick, forming part of a mass of twenty-five to fifty feet of superincumbent material. When this special stratum of sandy materials is washed, the diamonds have been found. I have taken steps to obtain an authentic crystal from this place, which appears to be the most prolific locality of the diamond yet observed in California.
In the first volume of the Geology of California, page 276, Mr. Rémond is quoted as authority for the existence of diamonds at Volcano. If this locality is distinct from that at Fiddletown, near Volcano, we have at present, five authenticated localities of the diamond in California, from which specimens have been identified by mineralogists.
If a knowledge of the characteristics of this remarkable species was more common among the miners who work in the deep gravel diggings, no doubt this gem would be found to be more abundant and in more numerous places than is now suspected.
San Francisco, May 6th, 1867.
Professor Whitney, in reply to various inquiries made by members, remarked that there were probably some fifteen or twenty different localities in California where diamonds had been found; but these were all of small size, the largest which had come under his notice weighing only 7¼ grains: this was found at French Corral, near San Juan North. It was difficult to give any directions by which miners could infallibly recognize the diamond when they happened to meet with this gem. The crystalline form is very different from that of quartz, which is now, however, much less frequently mistaken for the diamond than it was formerly. Most of the crystals found in California, up to this time, have been twenty-four sided. The fact that the faces of the crystals are usually curved instead of being plane surfaces, is also characteristic of the gem in question. The hardness and specific gravity are also sure guides; but miners rarely have the means of getting at either of these characters accurately. It is commonly believed that the diamond can be struck a heavy blow, on an anvil, without breaking; but this is a mistake, resulting from confounding toughness with hardness. It is extremely doubtful whether washing the gravel for diamonds in California would pay, under any circumstances; and it is believed that such washings are not remunerative anywhere, except when performed by slave or convict labor.