WILLEMITE, an important ore of zinc and a mineral of much mineralogical interest. It is essentially a zinc orthosilicate, hut all of the many varieties from Franklin Furnace and Ogdensburg, N. J., its two most prolific localities, contain considerable man ganese. The colors of the New Jersey wil lemite are very varied, white, green. yellow, flesh-red, brown and gray, the last three being characteristic of the variety troostite which occurs in crystals up to six inches in length. The crystallization of willemite is rhombohe dral, the common form being a hexagonal prism, either stout or much elongated, termi nated by obtuse rhombohedrons. It occurs in small crystals of prismatic or obtuse rhombo hedral habit in New Mexico. A granular form is also found in New Jersey in large quantities, intimately mixed with franklinite. Crystals from Belgium have an easy basal cleavage, but this cleavage is difficult in New Jersey crystals, which have eminent prismatic cleavage. The
mineral has a hardness of 5.5 and a specific gravity of 3.9 to 4.2. Transparent crystals and masses have been found in New Jersey which yield gems whose beauty is much enhanced by the strong double refraction of the mineral, though the inferior hardness precludes their use as jewels. Ordinarily willemite is opaque, but with transparent portions scattered through the mass. The green phosphorescence of wil lemite when struck with a hammer has been known for many years. During exposure to the Röntgen rays and to the ultra-violet and other rays of the Piffard lamp a gorgeous green fluorescence is observed in the New Jersey mineral and some specimens are also highly phosphorescent, but these properties are not possessed by willemite from other localities. Radium salts excite instant luminescence in the New Jersey mineral. These observations have attracted widespread interest.