ZINC AND MANGANESE DEPOSITS OF FRANKLIN FURNACE, N.J." 
By J. E. Wolff. 
According to a tradition, this celebrated occurrence of zinc and 
manganese ore was noticed and prospected as early as 1640, but Lord 
Sterling, after whom Sterling Hill is named, did the first mining in 
1774. About this time several tons of the red zinc oxide were shipped 
to London, yet the first description and analysis of this mineral were 
given by Dr. Bruce in 1810, and of franklinite by Berthier in 1819. 
The Mine Hill deposits were worked for iron ore about the beginning 
of the last century, but there was not much mining for zinc until 
after 1840. Different parts of the deposits have been worked more or 
less continuously since then by different companies and there has 
been long litigation, which has been finally settled by the consolida- 
tion of all the interests. The ores are now treated at the mines by 
magnetic separators, which separate the franklinite (as well as the 
garnet and other impurities) from the willemite and zincite, while the 
calcite is removed by jigging. The principal uses of the zinc ores are 
for metallic zinc and zinc white, and of the manganese for Bessemer 
steel. 
The ores occur at Mine Hill (Franklin Furnace) and Sterling Hill 
(Ogdensburg), localities 3 miles apart, and at no other place has 
exploration found more than traces of the ores. The deposit is in the 
white Franklin limestone, and at Mine Hill, where t lie surface and 
underground workings are best developed, lies about 30 feet from the 
gneiss boundary on the west, along the west limb. 
The ores consist of zincite, the red oxide of zinc (ZnO), containing 
94 per cent zinc oxide and 6 per cent manganese oxide; willemite, 
silicate of zinc (Zn 2 Si0 4 ), containing 67 to 69 per cent zinc oxide 
and 5 to 10 per cent manganese oxide; and franklinite (FeZnMn) O 
(FeMn) 2 3 , containing 56 to 67 per cent ferric oxide, 4 to 10 per cent 
manganese sesquioxide, 7 to 23 per cent zinc oxide, 10 to 16 per cent 
manganese oxide. The ores are usually accompanied by varying pro- 
portions of calcite. The contrast between the deep-red zincite, green 
willemite, lustrous black franklinite, and white calcite is very strik- 
ing. The proportions of these minerals vary constantly, so that 
sometimes zincite is abundant, sometimes only present in traces, and 
o From the descriptive text of the Franklin Furnace folio, Geologic Atlas of the United States- 
in preparation. 
214 
