26 NEW VOKK STATE MUSEUM 



igneous magna, (juitc similar in general features to the titanifcrous 

 magnetites that occur in gabbros and anorthosites. Some of the 

 deposits were worked in ilie early days for iron ore, but the ma- 

 terial proved too refractory for successful treatment in the fur- 

 nace. The emery is not regarded in the trade as equal to the 

 Grecian or Turkish product, though it is said to be very serviceable 

 when made into wheels with a vitreous bond. 



FELDSPAR 



The small demand lor felds])ar among pottery manufacturers 

 last year was reflected in a decreased output of the better grades 

 of the mineral, i. c. the potash feldspars free from iron or other 

 obnoxious impurities. On the other hand, the production of un- 

 selected feldspar, such as finds employment for roofing material, 

 poultry grit, abrasive purposes, etc. showed a substantial gain over 

 the quantity reported in 1907. 



The occurrence of pegmatite, from which feldspar is obtained. 

 is hmited in this State to the Adirondack Precambric area and the 

 southeastern region of crystalline rocks. The pegmatite forms dikes, 

 sheellike masses or irregular bodies, usually in association with 

 larger masses of allied intrusive rocks of which it often consti- 

 tutes but a coarser phase. Most occurrences have the composition 

 of granite, containing besides feldspar a considerable proportion 

 of quartz and smaller amounts of mica, hornblende or rarely 

 pyroxene. The presence of iron-bearing minerals has an impor- 

 tant bearing upon the quality of the product, since for pottery 

 purposes it is absolutely essential that the feldspar contain nothing 

 more than a trace of iron. When occurring in segregated particles 

 their elimination can be effected sometimes by careful cobbing. In 

 addition to those already enumerated, pyrite, magnetite and tour- 

 malin are among the iron-bearing minerals commonly found in 

 pegmatite. For pottery uses the potash feldspars (microcline and 

 orthoclase) are the only ones produced in New York State and 

 they seem to have the preference in that trade, though for what 

 reason is not well understood. The plagioclase feldspars are found 

 in the Adirondack pegmatites w^hich are chiefly quarried for roofing 

 material. 



The quarries now active in the State are situated in Westchester, 

 Essex and Saratoga counties. Those near Bedford, Westchester 

 CO. produce most of the pottery feldspar. They are operated by 

 P. H. Kinkel's Sons who grind a large part of the output before . 



