A
spray of acicular Millerite crystals on Calcite.
A cluster of Millerite sprays
from Nevada.
Millerite on Calcite MMT 319
from Tarragona, Spain
CHEMISTRY NiS Nickel sulfide
CRYSTALLOGRAPHY Hexagonal
CRYSTAL GROWTH AND HABITS Millerite most commonly forms as this filaments (capillary) in radiating sprays. It also forms fibrous mats and rarely is it granular to massive.
COLOR AND OTHER OPTICAL PROPERTIES Fresh Millerite is brass to bronze yellow but tarnishes to a slight greenish hue with iridescence.
HARDNESS 3 - 3.5
SPECIFIC GRAVITY 5.4 - 5.5
LUSTER Metallic
STREAK Greenish black
BREAKABILITY Perfect cleavage in 2 directions, uneven fracture, brittle, hairs are elastic
OCCURRENCE Millerite is normally found in low temperature hydrothermal carbonate veins and with barite.
ASSOCIATED MINERALS Calcite, Dolomite, Barite, Sphalerite, Pyrite, Galena, Nickeline