1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 127 



grains of free quartz. Sckoetensack* describes a "true jadeite" from 

 Monghoung, in Burniah, as being a homogeneous aggregate of large 

 granules and long curved lamellae, with the cleavage of pyroxene (87°), 

 and giving extinction angles of 35°. 



The last of the four Costa Eican specimens examined was the soft 

 dark green specimen from Las Huacas, No. 59899. In composition it is 

 as follows : 



Ignition 10.39 



Silica 70.49 



Alumina 11.39 



Ferrous oxide 2. 39 



Manganous oxide trace 



Lime 3.83 



Magnesia .57 



Alkalies undetermined 



99. 06 



A microscopic examination shows that the mineral is evidently a highly 

 altered volcanic tuff, but very difficult to make out. The mass of tbe 

 rock is made up of a greenish-gray amorphous felt, through which are 

 scattered rounded bunches of a bright green chlorite and small, colorless 

 points and elongated crystals, which may be felspathic, although they 

 are too small to show twin striee. There are also occasional colorless, 

 elongated, and curved shreds, which are wholly without action in polar- 

 ized light and which are doubtless glass. 



Two portions of a chambered shell of a minute rhizopod occur in the 

 slide. Not even by courtesy can this substance be classified as jade. 



Through the kindness of Mr. Thomas Wilson, whose collection fur- 

 nished the Eobenhausen nephrite already described, we have been en- 

 abled to examine several other worked specimens of minerals which 

 are sometimes classed, though loosely, with jade. They come from vari- 

 ous localities and may be briefly summarized as follows, in the order of 

 their specific gravity as determined by Dr. Hallock : 



No. 100365. Robenhausen, Lake Pfaffikon, Switzerland. Green, mottled saussu- 

 rite, specific gravity 3.418. 



No. 100586a. Same locality. Dark green saussurite, specific gravity 3.403. 



No. 100031. From Brittany. Ckloromelite ? Dark green, mottled, specific gravity 

 3.392. 



No. 100630. Yverdun, L. Neuchatel, Switzerland. Pale green adze, specific gravity 

 3.347. 



No. 100238. Brittany. Fibrolite, specific gravity 3.147. 



No. 100516. Estavayer, L. Neuchatel. Black, specific gravity 3.132. 



No. 100629. Yverdun. Green nephrite, specific gravity 3.028. 



No. 100586&. The Robenhausen nephrite already described, specilic gravity 3.015. 



No. 100670. L. Constance. Dark green nephrite, specific gravity 3.009. 



No. 100029. Brittany. Black mineral, specific gravity 2.705. 



Of these the fibrolite, 100238 ; the saussurite, 100586a ; and the 



* Op. cit.,]>. 7. 



