Allan Hills 84001
Allan Hills 84001 is a meteorite that was found in Allan Hills, Antarctica on December 27,1984 by a team of U. S. meteorite hunters from the ANSMET project. Like other members of the group of SNCs, ALH84001 is thought to be from Mars, however, it does not fit into any of the previously discovered SNC groups. On discovery, its mass was 1.93 kilograms. S, president Bill Clinton giving a speech about the potential discovery. This rock is considered to be one of the oldest Martian meteorites, based on chemical analyses, it is thought to have originated on Mars from a period when liquid water existed on the now arid planets surface. According to the analysis, Eos Chasma in the Valles Marineris canyon appears to be the source of the meteorite, the analysis was not conclusive, in part because it was limited to areas of Mars not obscured by dust. The theory holds that ALH84001 was blasted off from the surface of Mars by an impact about 17 million years ago. These dates were established by a variety of dating techniques, including samarium-neodymium, rubidium-strontium, potassium-argon.
Other meteorites that have potential biological markings have generated less interest because they do not contain rock from a wet Mars, ALH84001 is the only meteorite collected from such a time period. In October 2011 it was reported that isotopic analysis indicated that the carbonates in ALH84001 were precipitated at a temperature of 18 °C with water and carbon dioxide from the Martian atmosphere. On August 6,1996, ALH84001 became newsworthy when it was claimed that the meteorite may contain evidence of traces of life from Mars, under the scanning electron microscope structures were revealed that some scientists interpreted as fossils of bacteria-like lifeforms. The structures found on ALH84001 are 20–100 nanometres in diameter, similar in size to theoretical nanobacteria, the announcement of possible extraterrestrial life caused considerable controversy. David S. McKay at NASA argued that likely microbial terrestrial contamination found in other Martian meteorites does not resemble the shapes in the ALH84001.
In particular, the shapes within the ALH84001 look intergrown or embedded in the indigenous material, while likely contamination does not. While it has not yet conclusively been shown how the features in the meteorite were formed, David McKay says these results were obtained using unrealistically pure raw materials as a starting point, and will not explain many of the features described by us in ALH84001. According to McKay, a plausible inorganic model must explain all of the properties that we. The rest of the community disagreed with McKay. However, the consensus is that morphology alone cannot be used unambiguously as a tool for primitive life detection. Interpretation of morphology is notoriously subjective, and its use alone has led to errors of interpretation
Gabbro refers to a large group of dark, often phaneritic, mafic intrusive igneous rocks chemically equivalent to basalt. It forms when magma is trapped beneath the Earths surface. Much of the Earths oceanic crust is made of gabbro, formed at mid-ocean ridges, Gabbro is found as plutons associated with continental volcanism. Due to its variant nature, the term gabbro may be applied loosely to a range of intrusive rocks. The term gabbro was used in the 1760s to name a set of types that were found in the ophiolites of the Apennine Mountains in Italy. Then, in 1809, the German geologist Christian Leopold von Buch used the term more restrictively in his description of these Italian ophiolitic rocks and he assigned the name gabbro to rocks that geologists nowadays would more strictly call metagabbro. Von Buch named gabbro after Gabbro, a village in Rosignano Marittimo municipality of Tuscany, Gabbro is dense, greenish or dark-colored and contains pyroxene and minor amounts of amphibole and olivine.
The pyroxene content is mostly clinopyroxene, generally augite, but small amounts of orthopyroxene may be present, if the amount of orthopyroxene is more than 95% of the total pyroxene content, the rock is termed norite. On the other hand, gabbro has more than 95% of its pyroxenes in the form of the monoclinic clinopyroxene/s, the calcium rich plagioclase feldspar and pyroxene content vary between 10% - 90% in gabbro. If more than 90% plagioclase is present, the rock is an anorthosite, if on the other hand, the rock contains more than 90% pyroxenes, it is termed pyroxenite. Gabbro may contain amounts of olivine and biotite. The quartz content in gabbro is less than 5% of total volume, quartz gabbros or monzogabbros are known to occur, for example the cizlakite at Pohorje in northeastern Slovenia, and are probably derived from magma that was over-saturated with silica. Gabbros contain minor amounts, typically a few percent, of iron-titanium oxides such as magnetite, Gabbro is generally coarse grained, with crystals in the size range of 1 mm or greater.
Finer grained equivalents of gabbro are called diabase, although the term microgabbro is often used when extra descriptiveness is desired, Gabbro may be extremely coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are essentially coarse grained gabbro, some may exhibit acicular crystal habits. Gabbro is usually equigranular in texture, although it may be porphyritic at times, cumulate gabbros are more properly termed pyroxene-plagioclase adcumulate. Gabbro is an part of the oceanic crust, and can be found in many ophiolite complexes as parts of zones III. Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, mantle plume hypotheses may rely on identifying mafic and ultramafic intrusions and coeval basalt volcanism. It is better to base a rock definition on descriptive characteristics of the rather than how or where it was formed
Peridotite is a dense, coarse-grained igneous rock consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica and it is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from the Earths mantle, either as solid blocks and fragments, the compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite and amphibole. Peridotite is the dominant rock of the part of the Earths mantle. The word peridotite comes from the gemstone peridot, which consists of pale green olivine, classic peridotite is bright green with some specks of black, although most hand samples tend to be darker green. Peridotitic outcrops typically range from bright yellow to dark green in color. While green and yellow are the most common colors, peridotitic rocks may exhibit a range of colors such as blue, brown. Dunite, more than 90% olivine, typically with Mg/Fe ratio of about 9,1, mostly composed of olivine plus clinopyroxene.
Harzburgite, mostly composed of olivine plus orthopyroxene, and relatively low proportions of basaltic ingredients, most common form of peridotite, mostly composed of olivine and clinopyroxene, and have relatively high proportions of basaltic ingredients. Partial fusion of lherzolite and extraction of the melt fraction can leave a residue of harzburgite. Magnesium-rich olivine forms a proportion of peridotite, and so magnesium content is high. Layered igneous complexes have more varied compositions, depending on the fractions of pyroxenes, plagioclase. Minor minerals and mineral groups in peridotite include plagioclase, garnet, amphibole, in peridotite, plagioclase is stable at relatively low pressures, aluminous spinel at higher pressures, and garnet at yet higher pressures. Peridotite is the dominant rock of the Earths mantle above a depth of about 400 km, below that depth, olivine is converted to the higher-pressure mineral wadsleyite. Oceanic plates consist of up to about 100 km of peridotite covered by a thin crust, the crust, commonly about 6 km thick, consists of basalt and minor sediments.
The peridotite below the ocean crust, abyssal peridotite, is found on the walls of rifts in the sea floor. Oceanic plates are usually subducted back into the mantle in subduction zones, peridotites occur as fragments carried up by magmas from the mantle. Among the rocks that commonly include peridotite xenoliths are basalt and kimberlite, certain volcanic rocks, sometimes called komatiites, are so rich in olivine and pyroxene that they can be termed peridotite
A thin sliver of rock is cut from the sample with a diamond saw and ground optically flat. It is mounted on a slide and ground smooth using progressively finer abrasive grit until the sample is only 30 μm thick. The method involved using the Michel-Lévy interference colour chart, typically quartz is used as the gauge to determine thickness as it is one of the most abundant minerals. As different minerals have different optical properties, most rock forming minerals can be easily identified, plagioclase for example can be seen in the photo on the right as a clear mineral with multiple parallel twinning planes. The large blue-green minerals are clinopyroxene with some exsolution of orthopyroxene, thin sections are prepared in order to investigate the optical properties of the minerals in the rock. This work is a part of petrology and helps to reveal the origin, a photograph of a rock in thin section is often referred to as a photomicrograph. Fine-grained rocks, particularly those containing minerals of high birefringence, such as calcite, are prepared as ultra-thin sections.
An ordinary 30 μm thin section is prepared as described above, the section is polished on both sides using a fine diamond paste until it has a thickness in the range of 2-12 μm. This technique has been used to study the microstructure of fine-grained carbonates such as the Lochseitenkalk mylonite in which the grains are less than 5 μm in size. Ceramography, thin sections of ceramics Shelley, D
Feldspars are a group of rock-forming tectosilicate minerals that make up about 40% of the Earths continental crust. Feldspars crystallize from magma as veins in both intrusive and extrusive rocks and are present in many types of metamorphic rock. Rock formed almost entirely of plagioclase feldspar is known as anorthosite. Feldspars are found in types of sedimentary rocks. The name feldspar derives from the German Feldspat, a compound of the words Feld and Spat, the change from Spat to -spar was influenced by the English word spar, a synonym for mineral. Feldspathic refers to materials that contain feldspar, the alternate spelling, has largely fallen out of use. This group of minerals consists of tectosilicates, solid solutions between albite and anorthite are called plagioclase, or more properly plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two solid solutions, immiscibility occurs at temperatures common in the crust of the earth. Albite is considered both a plagioclase and alkali feldspar, the alkali feldspars are as follows, orthoclase —KAlSi3O8 sanidine —AlSi3O8 microcline —KAlSi3O8 anorthoclase —AlSi3O8 Sanidine is stable at the highest temperatures, and microcline at the lowest.
Perthite is a texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye, microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope. Barium feldspars are considered alkali feldspars, barium feldspars form as the result of the substitution of barium for potassium in the mineral structure. The barium feldspars are monoclinic and include the following, celsian—BaAl2Si2O8 hyalophane—4O8 The plagioclase feldspars are triclinic, the immiscibility gaps in the plagioclase solid solutions are complex compared to the gap in the alkali feldspars. The play of colours visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae, chemical weathering of feldspars results in the formation of clay minerals.
About 20 million tonnes of feldspar were produced in 2010, mostly by three countries, Italy and China, Feldspar is a common raw material used in glassmaking, and to some extent as a filler and extender in paint and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, in ceramics, the alkalis in feldspar act as a flux, lowering the melting temperature of a mixture. Fluxes melt at a stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers and other uses, such as fillers, accounted for the remainder
CheMin, short for Chemistry and Mineralogy, is an instrument located in the interior of the Curiosity rover that is exploring the surface of Gale crater on Mars. David Blake, from NASA Ames Research Center, is the Principal Investigator, CheMin identifies and quantifies the minerals present in rocks and soil delivered to it by the rovers robotic arm. By determining the mineralogy in rocks and soils, CheMin assesses the involvement of water in their formation, deposition, in addition, CheMin data is useful in the search for potential mineral biosignatures, energy sources for life or indicators for past habitable environments. CheMin aboard the Curiosity rover on Mars won the 2013 NASA Government Invention of the year award, CheMin is an X-ray powder diffraction instrument that has X-ray fluorescence capabilities. Raw CCD frames are processed into data products on board the rover to reduce the data volume and these data products are transmitted to Earth for further processing analyses. In operation, a collimated X-ray source produces and directs a beam through a sample cell containing powdered material.
An X-ray sensitive CCD imager is positioned on the side of the sample from the source. The CCD can measure the charge generated by each photon, diffracted X-rays strike the detector and are identified by their energy, producing a two-dimensional image that constitutes the diffraction pattern of the sample. Both crystalline and amorphous materials can be analyzed in this fashion, the funnel contains a 1 mm mesh screen to limit the particle size. Five permanent cells are loaded with calibration standards, these are single minerals or synthetic ceramic, each analysis may take up to 10 hours, spread out over two or more Martian nights. Capacity, CheMin is planned to analyze as many as 74 dry samples, cross-contamination by cell reuse is expected to be less than 5%. CheMin does not have the capability to store previously analyzed samples for reanalysis, detection limits, able to detect individual minerals that are present at the 3% level and above. The paragonetic tephra from a Hawaiian cinder cone has been mined to create Martian regolith simulant for researchers to use since 1998
A xenolith is a rock fragment which becomes enveloped in a larger rock during the latters development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement, a xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes, although the term xenolith is most commonly associated with igneous inclusions, a broad definition could include rock fragments which have become encased in sedimentary rock. Xenoliths are sometimes found in recovered meteorites and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites and lamprophyres, which have their source in the mantle, often contain fragments. Xenoliths of dunite and spinel lherzolite in basaltic lava flows are one example, kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition.
The aluminium-bearing minerals of these fragments provide clues to the depth of origin, calcic plagioclase is stable to a depth of 25 km. Between 25 km and about 60 km, spinel is the stable aluminium phase, at depths greater than about 60 km, dense garnet becomes the aluminium-bearing mineral. Some kimberlites contain xenoliths of eclogite, which is considered to be the high-pressure metamorphic product of basaltic oceanic crust, the large-scale inclusion of foreign rock strata at the margins of an igneous intrusion is called a roof pendant. Blatt and Robert J. Tracy
A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure.
Common distinguishing characteristics include crystal structure and habit, lustre, colour, tenacity, fracture, more specific tests for describing minerals include magnetism, taste or smell and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, disilicates, inosilicates, other important mineral groups include the native elements, oxides, carbonates and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which extensively involve mineralogy.
Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, crystals are periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
Zinc is a chemical element with the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table, in some respects zinc is chemically similar to magnesium, both elements exhibit only one normal oxidation state, and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earths crust and has five stable isotopes, the most common zinc ore is sphalerite, a zinc sulfide mineral. The largest workable lodes are in Australia and the United States, Zinc is refined by froth flotation of the ore and final extraction using electricity. Zinc metal was not produced on a large scale until the 12th century in India and was unknown to Europe until the end of the 16th century, the mines of Rajasthan have given definite evidence of zinc production going back to the 6th century BC. To date, the oldest evidence of pure zinc comes from Zawar, in Rajasthan, alchemists burned zinc in air to form what they called philosophers wool or white snow. The element was named by the alchemist Paracelsus after the German word Zinke.
German chemist Andreas Sigismund Marggraf is credited with discovering pure metallic zinc in 1746, work by Luigi Galvani and Alessandro Volta uncovered the electrochemical properties of zinc by 1800. Corrosion-resistant zinc plating of iron is the application for zinc. Other applications are in batteries, small non-structural castings. A variety of compounds are commonly used, such as zinc carbonate and zinc gluconate, zinc chloride, zinc pyrithione, zinc sulfide. Zinc is an essential mineral perceived by the public today as being of exceptional biologic and public health importance, Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children, deficiency causes growth retardation, delayed sexual maturation, infection susceptibility, enzymes with a zinc atom in the reactive center are widespread in biochemistry, such as alcohol dehydrogenase in humans. Consumption of excess zinc can cause ataxia and copper deficiency, Zinc is a bluish-white, diamagnetic metal, though most common commercial grades of the metal have a dull finish.6 pm.
The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C, above 210 °C, the metal becomes brittle again and can be pulverized by beating. Zinc is a conductor of electricity. For a metal, zinc has relatively low melting and boiling points, the melting point is the lowest of all the transition metals aside from mercury and cadmium. Many alloys contain zinc, including brass, Other metals long known to form binary alloys with zinc are aluminium, bismuth, iron, mercury, tin, cobalt, nickel and sodium
Augite is a common rock-forming pyroxene mineral with formula 2O6. The crystals are monoclinic and prismatic, augite has two prominent cleavages, meeting at angles near 90 degrees. Augite is a solution in the pyroxene group. Diopside and hedenbergite are important endmembers in augite, but augite can contain significant aluminium, with declining temperature, augite may exsolve lamellae of pigeonite and/or orthopyroxene. There is a miscibility gap between augite and omphacite, but this gap occurs at higher temperatures, there are no industrial or economic uses for this mineral. Augite is a mineral in mafic igneous rocks, for example and basalt. It occurs in relatively high-temperature metamorphic rocks such as mafic granulite and it commonly occurs in association with orthoclase, labradorite, leucite and other pyroxenes. Occasional specimens have an appearance that give rise to the minerals name. It was named by Abraham Gottlob Werner in 1792, transparent augites containing dendritic patterns are used as gems and ornamental stones known as shajar in parts of India.
It is found near the Ken River, local jewelers export raw shajar stone and items to different parts of India. Banda is one city noted for trade of shazar stone, fassaite Deer, W. A. Howie, R. A. and Zussman, J. An introduction to the rock-forming minerals
Martian soil is the fine regolith found on the surface of Mars. Its properties can differ significantly from those of terrestrial soil, the term Martian soil typically refers to the finer fraction of regolith. On Earth, the soil usually includes organic content. In contrast, planetary scientists adopt a definition of soil to distinguish it from rocks. Consequently, rocks classify as grains exceeding the size of cobbles on the Wentworth scale and this approach enables agreement across Martian remote sensing methods that span the electromagnetic spectrum from gamma to radio waves. ‘‘Soil’’ refers to all other, typically unconsolidated, material including those sufficiently fine-grained to be mobilized by wind, soil consequently encompasses a variety of regolith components identified at landing sites. Typical examples include, bedform armor, concretions, dust, rocky fragments, Martian dust generally connotes even finer materials than Martian soil, the fraction which is less than 30 micrometres in diameter.
Disagreement over the significance of soils definition arises due to the lack of a concept of soil in the literature. This definition emphasizes that soil is a body that retains information about its environmental history, Mars is covered with vast expanses of sand and dust and its surface is littered with rocks and boulders. The dust is occasionally picked up in vast planet-wide dust storms, Mars dust is very fine, and enough remains suspended in the atmosphere to give the sky a reddish hue. The sand is believed to move slowly in the Martian winds due to the very low density of the atmosphere in the present epoch. In the past, liquid water flowing in gullies and river valleys may have shaped the Martian regolith, Mars researchers are studying whether groundwater sapping is shaping the Martian regolith in the present epoch, and whether carbon dioxide hydrates exist on Mars and play a role. It is believed that large quantities of water and carbon dioxide ices remain frozen within the regolith in the parts of Mars.
Water contents of Martian regolith range from <2% by weight to more than 60%, the presence of olivine, which is an easily weatherable primary mineral, has been interpreted to mean that physical rather than chemical weathering processes currently dominate on Mars. High concentrations of ice in soils are thought to be the cause of accelerated soil creep, scientists compared the soil near Mars north pole to that of backyard gardens on Earth, and concluded that it could be suitable for growth of plants.3. The presence of the perchlorate, if confirmed, would make Martian soil more exotic than previously believed, while our understanding of Martian soils is extremely rudimentary, their diversity may raise the question of how we might compare them with our Earth-based soils. On October 17,2012, the first X-ray diffraction analysis of Martian soil was performed, hawaiian volcanic ash has been used as Martian regolith simulant by researchers since 1998. However, terrestrial contamination, as the source of the organic compounds, on September 26,2013, NASA scientists reported the Mars Curiosity rover detected abundant, easily accessible water in soil samples at the Rocknest region of Aeolis Palus in Gale Crater
Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye.
Intrusive rocks can be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, laccoliths and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface.
The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity