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DESCRIPTIVE MINERALOGY. 



Varieties. Ceylonitc or Pleonaste. This includes the dark green and black crystals, 

 which are translucent only on the edges. The other varieties are called Spinelle or Spinelle 

 Ruby. 



Composition. Red Spinelle — Alumina 74.50, silica 15.56, magnesia 8.25, oxide of iron 

 1.56, lime 0.75 (Klaproth). 



Black Spinelle from Amiti/, Orange county — Alumina 61. 79, silica 5 . 59, magnesia 17.87, 

 protoxide of iron 10 •56, lime 2.80, water 0.98 {Thomson). 



Geological Situation. In this State, spinelle is almost exclusively found in the white 

 limestone. It is frequently associated with other minerals. In other countries, it is usually 

 found in the sands of rivers. 



Use. Some of the varieties of spinelle are esteemed as gems. 



localities. 

 Jefferson County. Crystals of a light blue colour, associated with plumose mica, are 

 found in white limestone, two and a half miles southwest of the village of Oxbow in the town 

 of Antwerp. Similar ones have also been found in the immediate vicinity of the village. 

 The largest that have been observed, are half an inch in diameter. The forms are the pri- 

 mary (Fig. 255) ; the primary with the edges truncated, emargine of Hauy, Fig. 256, P on o 

 144° 48' 8", o on 120° ; the same with two opposite edges truncated, Fig. 257 ; and the 

 same, having four opposite sides extended so as to present the appearance of an octahedron 

 with a rectangular base. Fig. 258. 



Fig. 256. Fig. 257. Fig. 258. 



Orange County. Spinelle of various colours has been found more abundantly in this 

 county, than in any other part of the world. The specimens are sometimes also remarkable 

 for size, as they have been obtained measuring sixteen inches rOund the base. They are 

 most conunonly associated with brucite, and I believe invariably occur in white limestone. 



In the town of Cornwall, four miles west of West-Point, it occurs in black and green octa- 

 hedrons, thickly disseminated in white litaestone._ 



In the town of Monroe, in the Forest of Dean, at the Natural bridge, in the vicinity of 

 Greenwood furnace on Duck-cedar pond, and at the so called Silver mine, the black and 

 green varieties are found. They generally have the primary form. 



In the town of Warwick the localities are almost innumerable, although it is by no means 

 easy to obtain large or fine specimens at the present day. 



