Limestone alteration

Figure 7.29. A scatter plot of 813C and 8180 values of Holocene and Pleistocene carbonate sediments. Open circle, unlithified bulk Holocene sediments + s, lithified bulk Holocene sediment closed circles, Pleistocene limestones altered by meteoric water. For Pleistocene limestones altered in the meteoric environment, temperate climate samples are represented by 8180 values more enriched than -5%o, whereas tropical climate samples have 8180 values more depleted than -5%o. The large depletion in 13C is because the sediment samples are primarily from vadose environments. (After Land, 1986.)...

Quicklime and hydrated lime are reasonably stable compounds but not nearly as stable as their limestone antecedents. Chemically, quicklime is stable at any temperature, but it is extremely vulnerable to moisture. Even moisture in the air produces a destabilizing effect by air-slaking it into a hydrate. As a result, an active high calcium quicklime is a strong desiccant (qv). Probably hydrate is more stable than quicklime. Certainly hydrated lime is less perishable chemically because water does not alter its chemical composition. However, its strong affinity for carbon dioxide causes recarbonation. Dolomitic quicklime is less sensitive to slaking than high calcium quicklime, and dead-burned forms are completely stable under moisture-saturated conditions. 

Geology of the province is composed of Paleozoic basements. Tertiary altered submarine volcanic and sedimentary rocks (Green tuff) and Quaternary volcanic rocks. The basements are shale, tuff, limestone and chert of unknown ages. A simplified geologic map is shown in Fig. 1.148. 

Vecchioli, J., Ehrlich, G.G., Godsy, E.M., and Pascale, C.A., Alterations in the chemistry of an industrial waste liquid injected into limestone near Pensacola, Florida, in Hydrogeology ofKarstic Terrains, Case Histories, Vol. 1, Castany, G., Groba, E., and Romijn, E., Eds., International Association of Hydrogeologists, 1984, pp. 217-221. 

Limestone varieties differ greatly from one another in their texture and the impurities they contain, and consequently they also differ in color. The color of limestone may vary from white (when it contains practically no impurities) to off-white and even to intensely colored. Minor inclusions within the limestone structure are often of silica, usually in a concentration below 5%, as well as feldspar and clay in still lesser amounts. Many types of limestone also include embedded fossils. Much limestone deposits in the outer crust of the earth are altered during geologic metamorphic processes that involve mainly pressure and heat but also liquids and gases. Marble, for example, a metamorphic rock derived from calcium carbonate, is white when composed only of this substance colored metal ions and other impurities impart to marble a wide range of colors such as red, yellow, and green and also give... 

Acid rain harms the environment in a number of ways it dissolves many rocks and metals, alters the composition of soils, groundwaters, and lakes, and alters the environmental conditions of living organisms. Acid rain is also particularly harmful to ancient objects and structures, as it plays an important role in their deterioration and sometimes total destruction. Unprotected limestone, marble, and sandstone, all of them widely used in ancient times for building and making statuary, are disintegrated by acid rain, which... 

Argentite, natural occurrence of, 22 668 Argentium Sterling, 12 562 Argentothiosulfate complexes, 19 215 Argillaceous limestone, 15 26 Argillic alteration zones, gallium in,... 

The Silver Bell Mine area consists of dipping units that are composed of dacite porphyry, alaskite and monazite. The rock ages span the Paleozoic, Mesozoic and Cenozoic periods. The Paleozoic wall rocks consist of quartzite, siltstone and altered limestone. The carbonate rocks are exposed along the contact between the host rock and intrusions, and host the... 

In a limestone deposit at Kinnekulle, Sweden, a remarkable collection of more than 40 highly altered meteorites (Fig. 9.18) totaling 7.7 kg have been collected during routine guarrying operations (Schmitz etal., 1997,2001,2003). The 3.2-m-thick limestone layer in which they are found was deposited over -1.75 Myr in the mid-Ordovician. Despite being almost completely replaced by calcite, barite, and phyllosilicates, the meteorites are easily identified by their chondritic texture. Their identification as meteorites is confirmed by measurements of platinum-group elements. The chemical characteristics of relict spinels indicate that they are either L or LL chondrites. 

As I started to go down the slope, I was astonished to see the pond water begin to churn and to see the logs stand up on end in an impossible defiance of gravity and several other rules of physical mechanics Of course, the most obvious explanation of this experience—that I was in an altered state of consciousness—never occurred to me. Instead, and this is the resolution I spoke of above, the earth opened up and the pond water and the logs slid through the aperture into the psychedelic cavern that opened my story. It s a limestone cavern, I exclaimed to no one in particular as I ran down to examine its vast and exotic volume. 

Limestone and dolostone (localized gold-bearing hydrothermal alteration) Roberts Mountain Formation north-central Nevada, USA 10 samples... 

Zhabin, A.G., Samsonova, N.S., Chuchua, I.B. et al. (1990) Ore-bearing metasomatically altered limestones of the black shale association. International Geology Review, 32(11), 1145-55. 

I. Cahoon (19S4) hydrothermal alteration of dolomitic limestone, Milford, Utah, U.S.A. analyst W. Savournin. 

Weaver (1959) noted that the chlorite, which is a common constituent of the Ordovician K-bentonite beds of the eastern United States, has a dioctahedral 2 1 layer and a trioctahedral hydroxide sheet. A partial chemical analysis indicated the chlorite contained less than 2% Fe203. Both layers were probably formed in place from the alteration of volcanic ash in a marine environment. Only one other chlorite of this type had been detected in X-ray patterns of approximately 75,000 samples of sedimentary rocks. The other sample was from a Paleozoic argillaceous limestone at a depth of 24,400 ft. in Oklahoma. Chlorites of this type might well go undetected when chlorite is only a minor component. 

Because the bulk of the limestone volume of Bermuda has spent most of its existence in the vadose zone, much of the limestone mass shows the imprint of vadose diagenesis, and progressive depletion in 13C with increasing age. However, limestones older than 125,000 years have spent more time in the phreatic meteoric zone. These limestones are more extensively altered by freshwater and freshwater-seawater mixtures. Their relatively light 813C values, however, imply alteration in a relatively open system in which soil carbon dioxide, depleted in 13C because of oxidation of organic matter, was an important source of carbon for replacement reactions. 

The rate at which metastable phases dissolve or are replaced is an important problem in carbonate diagenesis. Carbonate mineral assemblages persist metastably in environments where they should have altered to stable assemblages. The question is "what are the time scales of these alterations" They are certainly variable ranging from a few thousand to a few hundreds of millions of years. Even calcites in very old limestones show chemical and structural heterogeneities, indicating that the stabilization of these phases is not complete. Unfortunately, it is difficult, but not impossible, to apply directly the lessons learned about carbonate mineral dissolution and precipitation in the laboratory to natural environments. 

Figure 7.35. Schematic diagram of mineral balance versus diagenetic time for vadose and phreatic meteoric alteration of Bermudian limestones. These trends are mainly based on stratigraphic analysis and hand specimen petrography and geochemistry. (After Land et al., 1967.)...

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