The principal mines explored at the present day, and whence most of our opals are now derived, are those of Hungary and Honduras. The Hungarian mines are of great extent and are now scientifically explored, but those of Central America are undetermined and but rudely mined. It is believed that there are other mines in Central America besides those of Honduras, for the natives at times bring fine specimens to the coast from localities widely separated. It is quite true that most of the opals of America are less hard than the Hungarian, but they are no less brilliant, and some of them withstand atmospheric effects and the wear of time quite as well. The Honduras opals are found near Gracias a Dios in porcelain earth, and are extracted in irregular masses, sometimes uniform or globular concretions, with rough and deeply indented surfaces. These masses do not exhibit the least tendency to crystallization like quartz, and they are generally quite small. Their natural colors are pale, and vary from brown to a pearly gray. They often exhibit a rich and varied play of the rainbow hues, even in their natural and rough condition. But sometimes, when this rough exterior is removed by the lapidary’s wheel, and the gem is highly polished, the colors vanish as if by magic. The polished stone no longer displays a single ray of the brilliant fires which illuminated every angle of the stone when in its rough state. This singular disappearance may be explained by the theory that the surface has been too highly polished, and the substance of the stone is rendered too transparent to permit the requisite degree of reflection, for when the surface is slightly roughened the play of colors again returns. The finest specimens are therefore those which are translucent, or those which, being transparent, are backed by an opaque ground which refracts the light. The opal-bearing districts in Central America are far more extensive than is generally supposed. The Province of Honduras abounds in them, and we have evidence of others occurring in the State of Guatemala on the Pacific coast. The following descriptions of some of the opal mines of Honduras were published by Dr. J. Le Conte, in 1868, in his report of the Inter-oceanic Railroad survey:--