Chalcocite, a copper sulfide mineral, was first reported from Franklin by Palache (1935) and has subsequently been found in additional assemblages at both Franklin and Sterling Hill. Although a significant local host for Cu, it is a minor mineral here and has no economic significance locally.
Chalcopyrite is bright brass-yellow, opaque, with metallic luster, and is differentiated from pyrite by its relatively inferior hardness. Specimens may be oxidized, displaying an iridescent tarnish.
Chalcopyrite is a minor accessory mineral of limited occurrence. It is commonly associated with sphalerite, galena, bornite, calcite, and other minerals, in both fine-grained and coarse-grained assemblages, occurring mostly in the Paleozoic sulfide veins. Masses up to 10 cm are known. Reflected-light studies by [Dunn] reveal that tennantite, bornite, and galena are minor constituents of many chalcopyrite veins. Where hot chalcopyrite has reacted with willemite-franklinite-calcite ore, the reactants are predominantly sphalerite and magnetite, which form a black, fine-grained, dense reaction zone. The association with magnetite is common at Franklin. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: CuFeS2
 Essential Elements: Copper, Iron, Sulfur
 All Elements in Formula: Copper, Iron, Sulfur
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
 To find out more about this mineral at minDat's website, follow this link   Chalcopyrite

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.531

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.49

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 35, No. 2 - Fall 1994, pg. 21A Complex Base-Metal Assemblage From the Sterling Mine New Jersey - Chalcopyrite

Chalcopyrite and calcite from Franklin, NJ
Chalcopyrite (brass yellow) and calcite (white to light gray) from Franklin, NJ. 4 1/4" x 2 1/4". From the collection of JVF, photo by WP.

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