The Mineral CHENGDEITE

Chemistry: Ir₃Fe, Iridium Iron
Class: Native Elements
Subclass: Native Metals
Group: Isoferroplatinum
Uses: A very minor ore of iridium and as mineral specimens.
Specimens

Chengdeite is one of the most dense minerals known. At a specific gravity of 19.3 it far exceeds all but a very few minerals. Gold is about 9% lighter at a lowly SG of 17.65 and platinum is slightly better at 18.00. Chengdeite in fact is only beat out by minerals that are more enriched in iridium and/or osmium; specifically the minerals iridium, osmium and iridosmine, an iridium/osmium alloy. Iridium, at a calculated density of 22.65 grams per cubic centimeter, is probably the densest element known to man. Although osmium, at 22.61 g/cubic cm, is close enough to make the distinction difficult. Most people think lead is the most dense! But at 11.37 g/cm3, its barely halfway there!

Chengdeite is classified as an element dispite the fact, that in chemical reality, it is a compound! Minerals like chengdeite are alloys with metallic bonds that are very similar to the more pure metallic elements and are thus classified as elements. Chengdeite is very rare and new to the mineral world. It is named for Chengde County, China from where it was discovered in placer deposits in just the early 1990's. Since then it has been found as a trace mineral in chromite rich ultra-mafic igneous deposits.

PHYSICAL CHARACTERISTICS:

Color is black.
Luster is metallic.
Transparency: Specimens are opaque.
Crystal System is isometric; bar 4 3 m.
Crystal Habits include nuggets found in placer deposits.
Cleavage is absent.
Fracture is hackly.
Hardness is 5
Specific Gravity is 19.3 (well above average, even for a metallic mineral)
Streak is black.
Associated Minerals include olivine, chromite and other ultra-mafic igneous minerals.
Notable Occurrences are limited to the type locality at Luan River in Chengde County, China and just a few ultra-mafic igneous rock deposits.
Best Field Indicator is crystal habit, color, locality and especially density.