In general, igneous, metamorphic and sedimentary processes do not appear to strongly fractionate Cu isotopes, while δCu values of Cu minerals vary widely. The average Cu isotopic composition of bulk silicate Earth has been measured as 0.06 ± 0.20‰ based on 132 different terrestrial samples. MORBs and oceanic island basalts (OIBs) generally have homogenous Cu isotopic compositions that fall around 0‰, while arc and continental basalts have more heterogeneous Cu isotope compositions that range from -0.19 to +0.47‰. These Cu isotope ratios of basalts suggest that mantle partial melting imparts negligible Cu isotopic fractionation, while recycling of crustal materials leads to widely variable δCu values. The Cu isotope compositions of copper-containing minerals vary over a wide range, likely due to alteration of the primary high-temperature deposits. In one study that investigated Cu isotopic compositions of various minerals from hydrothermal fields along the mid-Atlantic ridge, chalcopyrite from mafic igneous rocks had δCu values of -0.1 to -0.2‰, while Cu minerals in black smokers (chalcopyrite, bornite, covellite and atacamite) exhibited a wider range of δCu values from -1.0 to +4.0‰. Additionally, atacamite lining the outer rims of black smokers can be up to 2.5‰ heavier than chalcopyrite contained within the black smoker. δCu values of Cu minerals (including chrysocolle, azurite, malachite, cuprite and native copper) in low-temperature deposits have been observed to vary widely over a range of -3.0 to +5.6‰.