P L. Smedley, D.G. Kinniburgh/ Applied Geochemistry 17(2002 )517-568 Table 3 Typical As concentrations in common rock-forming minerals As concentration range(mg kg") References 0-77,000 Baur and Onishi(1969); Boyle and Jonasson(1973 Marcasite Dudas(1984): Fleet and Mumin(1997) Baur and Onishi(1969) 10-5000 Baur and Onishi (1969) Oxide up to 160 Baur and Onishi(19 Fe oxide(undifferentiated) up to 2000 Fe(ll) oxyhydroxide Pichler et al. (1999) Magnetite Baur and Onishi(1969) bartz 0.4-1.3 Baur and Onishi (1969) Feldspar Biotite amphibole BBBB uuuu dddd 0.05-0.8 Baur and Onishi(1969) Boyle ar n(1973) Boyle ar n(1973) on(1973) Sulphate minerals Gypsum/ anhydrite 1-6 Boyle and Barite Boyle and Jarosite 34-1000 Boyle and Other minerals Apatite 1-1000 Baur and Onishi(1969) Boyle and Jonasson(1973) Halite Stewart(1963 Fluorite Boyle and Jonasson(1973) round 1 mg kg-I or less. Carbonate minerals usually of high-As waters(Nicolli et al., 1989; Smedley et al contain less than 10 mg kg-I As(Table 3). 2002). This may relate to the reactive nature of recent acidic volcanic material, especially fine-grained ash and 3. 2. Rocks sediments and so its tendency to give rise to Na-rich high-pH ground waters(Section 5) 3.2.1. Igneous rocks Arsenic concentrations in igneous rocks are 3. 2.2. Metamorphic rocks low. Ure and Berrow (1982)quoted an average value of Arsenic concentrations in metamorphic rocks tend to 1.5 mg kg- for all igneous rock types(undisting reflect the concentrations in their igneous and sedimen- Averages for different types distinguished by silica con- tary precursors. Most contain around 5 mg kg- or less tent (Table 4) are slightly higher than this value but Pelitic rocks(slates, phyllites) typically have the highest generally less than 5 mg kg. volcanic glasses are only concentrations with on average ca 18 mg kg(Table 4) an averag (Table 4). Overall, there is relatively little difference 3.2.3. Sedimentary rocks between the different igneous rock types. Despite not The concentration of As in sedimentary rocks is typi- especially ashes, are often implicated in the generation slightly above average terrestrial abundance. Averagearound 1mg kg
1 or less. Carbonate minerals usually contain less than 10 mg kg
1 As (Table 3). 3.2. Rocks, sediments and soils 3.2.1. Igneous rocks Arsenic concentrations in igneous rocks are generally low. Ure and Berrow (1982) quoted an average value of 1.5 mg kg
1 for all igneous rock types (undistinguished). Averages for different types distinguished by silica con￾tent (Table 4) are slightly higher than this value but generally less than 5 mg kg
1 . Volcanic glasses are only slightly higher with an average of around 5.9 mg kg
1 (Table 4). Overall, there is relatively little difference between the different igneous rock types. Despite not having exceptional concentrations of As, volcanic rocks, especially ashes, are often implicated in the generation of high-As waters (Nicolli et al., 1989; Smedley et al., 2002). This may relate to the reactive nature of recent acidic volcanic material, especially fine-grained ash and its tendency to give rise to Na-rich high-pH ground￾waters (Section 5). 3.2.2. Metamorphic rocks Arsenic concentrations in metamorphic rocks tend to reflect the concentrations in their igneous and sedimen￾tary precursors. Most contain around 5 mg kg
1 or less. Pelitic rocks (slates, phyllites) typically have the highest concentrations with on average ca. 18 mg kg
1 (Table 4). 3.2.3. Sedimentary rocks The concentration of As in sedimentary rocks is typi￾cally in the range 5–10 mg kg
1 (Webster, 1999), i.e. slightly above average terrestrial abundance. Average Table 3 Typical As concentrations in common rock-forming minerals Mineral As concentration range (mg kg
1 ) References Sulphide minerals: Pyrite 100–77,000 Baur and Onishi (1969); Arehart et al. (1993); Fleet and Mumin (1997) Pyrrhotite 5–100 Boyle and Jonasson (1973); Marcasite 20–126,000 Dudas (1984); Fleet and Mumin (1997) Galena 5–10,000 Baur and Onishi (1969) Sphalerite 5–17,000 Baur and Onishi (1969) Chalcopyrite 10–5000 Baur and Onishi (1969) Oxide minerals Haematite up to 160 Baur and Onishi (1969) Fe oxide (undifferentiated) up to 2000 Boyle and Jonasson (1973) Fe(III) oxyhydroxide up to 76,000 Pichler et al. (1999) Magnetite 2.7–41Baur and Onishi (1969) Ilmenite <1Baur and Onishi (1969) Silicate minerals Quartz 0.4–1.3 Baur and Onishi (1969) Feldspar <0.1–2.1 Baur and Onishi (1969) Biotite 1.4 Baur and Onishi (1969) Amphibole 1.1–2.3 Baur and Onishi (1969) Olivine 0.08–0.17 Baur and Onishi (1969) Pyroxene 0.05–0.8 Baur and Onishi (1969) Carbonate minerals Calcite 1–8 Boyle and Jonasson (1973) Dolomite <3 Boyle and Jonasson (1973) Siderite <3 Boyle and Jonasson (1973) Sulphate minerals Gypsum/anhydrite <1–6 Boyle and Jonasson (1973) Barite <1–12 Boyle and Jonasson (1973) Jarosite 34–1000 Boyle and Jonasson (1973) Other minerals Apatite <1–1000 Baur and Onishi (1969), Boyle and Jonasson (1973) Halite <3–30 Stewart (1963) Fluorite <2 Boyle and Jonasson (1973) 530 P.L. Smedley, D.G. Kinniburgh / Applied Geochemistry 17 (2002) 517–568