b'Pyritethe firestoneFeatureFigure 11.Crossplot of air dried values of EM conductivity and bulk density for the 36 pyritic samples in Table 3. Overall, conductivity increases with density. Single crystal conductivities are quite high (1000s S/m) and exceed the modal value for n type pyrite (1000 S/m; Shuey 1975). Aggregated pyrite in massive form has a diminished conductivity (10s to 100s S/m) owing to grain boundary and other effects. The massive fresh pyrite set (#515) is shown in three groups one of which with high porosity (#1115) matches the low porosity trend (#6, 7, 10) in conductivity presumably because of better grain to grain suturing. Conductivity in the massive types is reduced by the presence of minor sphalerite and silicates (#1618) and still further by alteration (#19, 36). Banded and blebby pyritic metasediments have quite low conductivities (few S/m, or less). Minor chalcopyrite content (#24, 34, 35) boosts pyrite conductivity, and even more so does minor pyrrhotite (#2023). The red shaded area suggests a range of conductivity that may be encountered in massive, variably porous pyrite devoid of chalcopyrite and pyrrhotite. Pyrite, apart from the single crystals, is not very conductive, at least in the set of samples documented here. Included for comparison are a massive chalcopyrite (C) from siltstones of the Cobar Group NSW and a massive pyrrhotite (K) from an ultramafic environment at Kambalda WA. Both are significantly more conductive than the massive pyrite tested here. The pyrite data are deemed instructive and indicative, but by no means definitive of all varieties of pyrite.powdery melanterite, FeS0 47H 2 0, on grain boundaries and ininvolvement in, and contributions to, culture, industry, materials cracks, together with an acrid smell will serve to identify it. Inscience, geoscience, and, indeed, to life itself. It has been an limited measurements the writer carried out on clearly alteringimpressive set of physical properties which merit appreciation, material, conductivity seems to be of the order of a few S/m,and it warrants continuing study, especially as to its electrical Harvey (1928) measured three samples with conductivitiesproperties. Pyrite, the firestone, historically and currently is a ranging from 10 to 1000 S/m, presumably on fresh polishedvery important mineral. Pyrite matters. It is advantageous for surfaces. Unfortunately fresh unaltered marcasite could not begeoscientists to know if it is about, for one reason or another, for located to include in the measurements made for this article. better or for worse.Concluding remarks AcknowledgementsA blend of tough iron and soft sulphur could be expectedSusan Franks prepared the manuscript text, Emilija Kalnins to yield an interesting substance. The covalent chemicalsupplied the photography and the design in Figure 5, Lainie combination, as a disulphide, of these two disparate elementsKalnins helped with Figure 5 and the photography, David does not disappoint. For humankind pyrite has been, andKalnins provided considerable assistance in editing, design, continues to be, a very significant mineral because of itsand the layout of the figures. Dr Denis Lynch (CSIRO emeritus) 63 PREVIEW DECEMBER 2019'