Rock Density

Various rock types and individual minerals which constitute the Earth each have their characteristic range of densities. The distribution in the subsurface of the constituent rock types and minerals will therefore, be reflected through changes in the local gravitational field. The variation, from place to place, of the gravitational field of the Earth may, therefore, be interpreted in terms of the subsurface geology — with certain assumptions and limitations.

Gravimetric surveys are one of the fundamental means available to the geoscientist, to map the distribution of the subsurface geology, for both scientific and economic objectives. The following Table provides a list of typical rock types and minerals, with their density range and mean values. From this Table, it can be seen that the entire range of densities covers a factor of about eight— from 1.0 g/cm3 for water to 8.1 g/cm3 for cinnabar. There is considerable overlap between rock types, although in general, sediments are lower in density than igneous or metamorphic rocks, and acidic rocks are lower than mafic rocks.

Metallic minerals occupy the high end of the range, and when present in substantial amounts, in a deposit, they may facilitate the detection of that deposit through gravity measurements.

Densities of Typical Rock Types and Minerals
Rock Type Range (g/cm3) Average (g/cm3)   Mineral  Range (g/cm3) Average (g/cm3)
Sediments(wet)       Metallic minerals    
Overburden   1.92   Oxides, carbonates    
Soil 1.2 – 2.4 1.92   Bauxite 2.3 – 2.55 2.45
Clay 1.63 – 2.6 2.21   Limonite 3.5 – 4.0 3.78
Gravel 1.70 – 2.40 2.00   Siderite 3.7 – 3.9 3.83
Sand 1.70 – 2.30 2.00   Rutile 4.18 – 4.3 4.25
Sandstone 1.61 – 2.76 2.35   Manganite 4.2 – 4.4 4.32
Shale 1.77 – 3.20 2.40   Chromite 4.3 – 4.6 4.36
Limestone 1.93 – 2.90 2.55   Ilmenite 4.3 – 5.0 4.67
Dolomite 2.28 – 2.90 2.70   Pyrolusite 4.7 – 5.0 4.82
Sedimentary rocks (av.)   2.50   Magnetite 4.9 – 5.2 5.12
        Franklinite 5.0 – 5.22 5.12
Igneous rocks       Hematite 4.9 – 5.3 5.18
Rhyolite 2.35 – 2.70 2.52   Cuprite 5.7 – 6.15 5.92
Andesite 2.40 – 2.80 2.61   Cassiterite 6.8 – 7.1 6.92
Granite 2.50 – 2.81 2.64   Wolframite 7.1 – 7.5 7.32
Granodiorite 2.67 – 2.79 2.73   Sulfides, arsenides    
Porphyry 2.60 – 2.89 2.74   Sphalerite 3.5 – 4.0 3.75
Quartzdiorite 2.62 – 2.96 2.79   Malachite 3.9 – 4.03 4
Diorite 2.72 – 2.99 2.85   Chalcopyrite 4.1 – 4.3 4.2
Lavas 2.80 – 3.00 2.90   Stannite 4.3 – 4.52 4.4
Diabase 2.50 – 3.20 2.91   Stibnite 4.5 – 4.6 4.6
Basalt 2.70 – 3.30 2.99   Pyrrhotite 4.5 – 4.8 4.65
Gabbro 2.70 – 3.50 3.03   Molybdenite 4.4 – 4.8 4.7
Peridotite 2.78 – 3.37 3.15   Marcasite 4.7 – 4.9 4.85
Acid igneous 2.30 – 3.11 2.61   Pyrite 4.9 – 5.2 5
Basic igneous 2.09 – 3.17 2.79   Bornite 4.9 – 5.4 5.1
        Chalcocite 5.5 – 5.8 5.65
Metamorphic rocks       Cobaltite 5.8 – 6.3 6.1
Quartzite 2.50 – 2.70 2.60   Arsenopyrite 5.9 – 6.2 6.1
Schists 2.39 – 2.90 2.64   Bismuththinite 6.5 – 6.7 6.57
Graywacke 2.60 – 2.70 2.65   Galena 7.4 – 7.6 7.5
Marble 2.60 – 2.90 2.75   Cinnabar 8.0 – 8.2 8.1
Serpentine 2.40 – 3.10 2.78        
Slate 2.70 – 2.90 2.79   Non – metallic minerals    
Gneiss 2.59 – 3.00 2.80   Petroleum 0.6 – 0.9  
Amphibolite 2.90 – 3.04 2.96   Ice 0.88 – 0.92  
Eclogite 3.20 – 3.54 3.37   SeaWater 1.01 – 1.05  
Metamorphic 2.40 – 3.10 2.74   Lignite 1.1 – 1.25 1.19
        Softcoal 1.2 – 1.5 1.32
        Anthracite 1.34 – 1.8 1.5
        Chalk 1.53 – 2.6 2.01
        Graphite 1.9 – 2.3 2.15
        Rocksalt 2.1 – 2.6 2.22
        Gypsum 2.2 – 2.6 2.35
        Kaolinite 2.2 – 2.63 2.53
        Orthoclase 2.5 – 2.6  —
        Quartz 2.5 – 2.7 2.65
        Calcite 2.6 – 2.7  —
        Anhydrite 2.29 – 3.0 2.93
        Biotite 2.7 – 3.2 2.92
        Magnesite 2.9 – 3.12 3.03
        Fluorite 3.01 – 3.25 3.14
        Barite 4.3 – 4.7 4.47

Notes & Handouts

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