Other sedimentary rocks

If substantial arsenic is present in a sandstone or conglomerate, it may occur in hematite or other iron (oxy)(hydr)oxide cements or coatings on mineral grains. Arsenic may also be enriched in sandstones, conglomerates, and other clastic sedimentary rocks if hydrothermal or other secondary sulfide minerals are present (e.g. St. Peter Sandstone, (Gotkowitz et al., 2001) arsenian pyrite cement in the Marshall Sandstone of the Michigan Basin, USA, (Kolker et al., 2000 Szramek, Walter and McCall, 2004)). Sections of the St. Peter Sandstone in eastern Wisconsin, USA, are enriched in sulfide minerals and contain about 500 mg kg-1 of arsenic. In contrast, unmineralized portions typically have 10 mg kg-1 (Gotkowitz et al., 2001). If present in sedimentary rocks, hydrothermal sulfide deposits often tend to concentrate in veins and faults more than the rock matrices. 

Some limestones and dolostones are relatively rich in arsenic because they contain significant hydrothermal or diagenetic sulfide minerals. In particular, the Suwannee Limestone of Florida, USA, contains up to 54 mg kg-1 of arsenic (Table 3.23). Almost all of the arsenic is associated with diagenetic pyrite. The pyrites typically contain 100-11 200 mg kg-1 of arsenic (an average of 2300 mg kg-1 for 25 samples) (Price and Pichler, 2006). 

Salt deposits or evaporites precipitate from evaporating seawater that becomes trapped in semi-isolated marine basins. Salty desert lakes, such as Great Salt Lake, Utah, USA, or those in Death Valley, California, USA, are also sites of evaporite deposition. Common salt minerals include halite (NaCl), sylvite (KC1), 

Phosphorites are sedimentary rocks that contain at least 15-20 wt % P2O5 (Boggs, 1995), 266. The phosphate in phosphorites primarily occurs as apatite (Ca5(P04)3(F,Cl,0H)). Typically, phosphorites chemically precipitate in deep, cold marine waters. Due to chemical similarities, arsenate may partially substitute for phosphate and the arsenic concentrations of phosphorites may exceed 100 mg kg-1 ((Matschullat, 2000), 299 Table 3.23). However, arsenic concentrations in some phosphorites (e.g. southeast Jordan) are relatively low (7-9 mg kg-1) and the arsenic is mostly associated with clay and carbonate minerals rather than phosphates (Al-Hwaiti, Matheis and Saffarini, 2005). 

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Figure 10.5. Mass-age distribution of carbonate rocks and other sedimentary rock types plotted as survival rate (S) versus age. Total rock mass data from Gregor (1985) and estimates of carbonate rock mass from Table 10.1.

As might be anticipated, the trends observed for lithologic types versus age are reflected in trends in the chemistry and mineralogy of carbonates and other sedimentary rocks. Discussion of some of these latter trends, emphasizing first the overall trends for the past 3.8 billion years, then those of the Phanerozoic, are presented below. 

With sedimentary rocks radionuclides may also interact in different ways. They may be sorbed on sandstone, limestone and other sedimentary rocks. Heterogeneous exchange may contribute to the sorption, e.g. exchange of (aq) for... 

Piper D. Z. (1994) Seawater as the source of minor elements in black shales, phosphorites and other sedimentary rocks. Chenu Geol. 114, 95—114. 

Shale partings and split coal are terms applied to a coal seam that cannot be mined as a single unit because it is separated from the main stream by a parting of other sedimentary rock (Figure 1.2). 

Sedimentary rocks are classified depending on how they were formed. They are divided into four groups (a) clastic sedimentary rocks , (b) biochemical (or biogenic) sedimentary rocks, (c) chemical sedimentary rocks and (d) other sedimentary rocks formed by impact, volcanism and other processes. 

Authigenic A mineral or other sedimentary rock component that forms in place, rather than having been transported. May form either at the time the sedimentary rock was deposited or sometime after deposition by diagenetic processes. 

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