Quartz is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral behind feldspar. Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral; the transformation from α-quartz to β-quartz takes place abruptly at 573 °C. Since the transformation is accompanied by a significant change in volume, it can induce fracturing of ceramics or rocks passing through this temperature threshold. There are many different varieties of quartz. Since antiquity, varieties of quartz have been the most used minerals in the making of jewelry and hardstone carvings in Eurasia; the word "quartz" is derived from the German word "Quarz", which had the same form in the first half of the 14th century in Middle High German in East Central German and which came from the Polish dialect term kwardy, which corresponds to the Czech term tvrdý.
The Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning "icy cold", because some philosophers believed the mineral to be a form of supercooled ice. Today, the term rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the trigonal crystal system; the ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end. In nature quartz crystals are twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals form in a'bed' that has unconstrained growth into a void. However, doubly terminated crystals do occur where they develop without attachment, for instance within gypsum. A quartz geode is such a situation where the void is spherical in shape, lined with a bed of crystals pointing inward. Α-quartz crystallizes in the trigonal crystal system, space group P3121 or P3221 depending on the chirality.
Β-quartz belongs to space group P6222 and P6422, respectively. These space groups are chiral. Both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks; the transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, without change in the way they are linked. Although many of the varietal names arose from the color of the mineral, current scientific naming schemes refer to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, has been used for hardstone carvings, such as the Lothair Crystal. Common colored varieties include citrine, rose quartz, smoky quartz, milky quartz, others; these color differentiation's arise from chromophores which have been incorporated into the crystal structure of the mineral.
Polymorphs of quartz include: α-quartz, β-quartz, moganite, cristobalite and stishovite. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties; the cryptocrystalline varieties are either translucent or opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz including contrasting bands or patterns of color, are agate, carnelian or sard, onyx and jasper. Amethyst is a form of quartz that ranges from a dull purple color; the world's largest deposits of amethysts can be found in Brazil, Uruguay, France and Morocco. Sometimes amethyst and citrine are found growing in the same crystal, it is referred to as ametrine. An amethyst is formed. Blue quartz contains inclusions of fibrous crocidolite. Inclusions of the mineral dumortierite within quartz pieces result in silky-appearing splotches with a blue hue, shades giving off purple and/or grey colors additionally being found.
"Dumortierite quartz" will sometimes feature contrasting light and dark color zones across the material. Interest in the certain quality forms of blue quartz as a collectible gemstone arises in India and in the United States. Citrine is a variety of quartz whose color ranges from a pale yellow to brown due to ferric impurities. Natural citrines are rare. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a natural citrine's cloudy or smokey appearance, it is nearly impossible to differentiate between cut citrine and yellow topaz visually, but they differ in hardness. Brazil is the leading producer of citrine, with much
A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, petrified wood, coal, DNA remnants; the totality of fossils is known as the fossil record. Paleontology is the study of fossils: their age, method of formation, evolutionary significance. Specimens are considered to be fossils if they are over 10,000 years old; the oldest fossils are around 3.48 billion years old to 4.1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils; the development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host. There are many processes that lead to fossilization, including permineralization and molds, authigenic mineralization and recrystallization, adpression and bioimmuration.
Fossils vary in size from one-micrometre bacteria to dinosaurs and trees, many meters long and weighing many tons. A fossil preserves only a portion of the deceased organism that portion, mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may consist of the marks left behind by the organism while it was alive, such as animal tracks or feces; these types of fossil are called trace ichnofossils, as opposed to body fossils. Some fossils are called chemofossils or biosignatures; the process of fossilization varies according to external conditions. Permineralization is a process of fossilization; the empty spaces within an organism become filled with mineral-rich groundwater. Minerals precipitate from the groundwater; this process can occur in small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce detailed fossils. For permineralization to occur, the organism must become covered by sediment soon after death, otherwise decay commences.
The degree to which the remains are decayed when covered determines the details of the fossil. Some fossils consist only of skeletal teeth; this is a form of diagenesis. In some cases, the original remains of the organism dissolve or are otherwise destroyed; the remaining organism-shaped hole in the rock is called an external mold. If this hole is filled with other minerals, it is a cast. An endocast, or internal mold, is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a skull; this is a special form of mold formation. If the chemistry is right, the organism can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it. If this happens before significant decay to the organic tissue fine three-dimensional morphological detail can be preserved. Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization.
Replacement occurs. In some cases mineral replacement of the original shell occurs so and at such fine scales that microstructural features are preserved despite the total loss of original material. A shell is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, as from aragonite to calcite. Compression fossils, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case the fossil consists of original material, albeit in a geochemically altered state; this chemical change is an expression of diagenesis. What remains is a carbonaceous film known as a phytoleim, in which case the fossil is known as a compression. However, the phytoleim is lost and all that remains is an impression of the organism in the rock—an impression fossil. In many cases, however and impressions occur together. For instance, when the rock is broken open, the phytoleim will be attached to one part, whereas the counterpart will just be an impression.
For this reason, one term covers the two modes of preservation: adpression. Because of their antiquity, an unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, including blood vessels, the isolation of proteins and evidence for DNA fragments. In 2014, Mary Schweitzer and her colleagues reported the presence of iron particles associated with soft tissues recovered from dinosaur fossils. Based on various experiments that studied the interaction of iron in haemoglobin with blood vessel tissue they proposed that solution hypoxia coupled with iron chelation enhances the stability and preservation of soft tissue and provides the basis for an explanation for the unforeseen preservation of fossil soft tissues. However, a older study based on eight taxa ranging in time from the Devonian to the Jurassic found that reasonably well-preserved fibrils that represent collagen were preser
The Rhynie chert is an Early Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness. It is exposed near the village of Rhynie, Scotland; the Rhynie chert contains exceptionally preserved plant, fungus and animal material preserved in place by an overlying volcanic deposit. The bulk of the fossil bed consists of primitive plants, along with arthropods, lichens and fungi; this fossil bed is remarkable for two reasons. First, the age of the site places it at an early stage in the colonisation of land. Second, these cherts are famous for their exceptional state of ultrastructural preservation, with individual cell walls visible in polished specimens. Stomata have been counted and lignin remnants detected in the plant material, the breathing apparatus of trigonotarbids—of the class Arachnida— can be seen in cross-sections. Fungal hyphae can be seen acting as decomposers and mycorrhizal symbionts; the bed is under at least 1 metre of overburden, in a small field near the village of Rhynie, so is inaccessible to collectors.
A second unit, the Windyfield chert, is some 700 m from the Rhynie. The Rhynie chert extends for at least 80 m along 90 m down-dip; the chert was discovered by William Mackie while mapping the western margin of the Rhynie basin in 1910–1913. Trenches were cut into the chert at the end of this period, Robert Kidston and William Henry Lang worked furiously to describe the plant fossils between 1917 and 1921; the arthropods were examined soon afterwards by different workers. Interest in the chert waned until the field was reinvigorated by Alexander Geoffrey Lyon in the late 1950s, new material was collected by further trenching from 1963 to 1971. Since 1980, the chert has been examined by the University of Münster, from 1987 by Aberdeen University, whose researchers confirmed that the chert was indeed produced in a hot spring setting. Cores, allowing an insight into the evolution of the chert over time, were drilled in 1988 and 1997, accompanied by further trenching efforts, which unearthed the Windyfield chert.
Until the Rhynie chert was the only such deposit known from the geological record, although recent work has turned up other localities from different time periods and continents. The chert was formed when silica-rich water from volcanic springs rose and petrified the early terrestrial ecosystem, in situ and instantaneously, in much the same fashion that organisms are petrified by hot springs today - although the astounding fidelity of preservation has not been found in recent deposits. Hot springs, with temperatures between 90 to 120 °C, were active in a number of episodes, their activity is preserved in 53 beds, 80 mm thick on average, over a 35.41 m sequence, interbedded with sands and tuffs - which speak of local volcanic activity. Deposition was rapid; the fluids originated from a shallowly dipping extensional fault system to the west, which bounded an extensional half-graben. Fossils were formed as silica formed in the hot springs themselves; the texture of the sinter formed resemble those found today in freshwater streams at Yellowstone which are alkaline and tepid 20 to 28 °C.
The springs were periodically active, flowed into an alluvial plain containing small lakes. By analogy with Yellowstone, the chert itself formed in a marshy area towards the latter end of the extent of outwash from the springs. Living vegetation covered around 55% of the land area, with litter covering 30% and the remaining 15% of the ground being bare. A braided river flowing to the north periodically deposited the sandy layers found in cores when it flooded its banks. Sedimentary textures which appear to have formed in the hydrothermal vents themselves are preserved with a brecciated texture. Spores collected from within surrounding rocks had been heated to different degrees, implying a complex history of local heating by volcanic processes; the preservation of plants varies from perfect three-dimensional cellular permineralisation to flattened charcoal films. On occasion, plants may have their vertical axes preserved in growth position, with rhizoids still attached to rhizomes. Plants were only found on the land - none lived in the water of lakes or hot springs.
Rhynia grew on sandy surfaces, is preserved there in life position. These two colonisers were subsequently joined by other genera; the time between sinter deposition events was too short to allow the populations to develop to climax communities, correspondingly early colonisers appear most pseudo-randomly, in logged sequences. Plants demonstrate best the great value of the exceptional preservation of the Rhynie chert; the presence of soft tissue, including parenchyma, is not observed elsewhere in the fossil record until the advent of amber in the Triassic. This allows the study of structures such as the air spaces behind stomata, whereas the conventional record at its best allows no more than the counting of stomata, it has enabled paleobotanists to d
Girolamo Segato was an Italian naturalist, cartographer and anatomist. He is best known for his work in the artificial petrifaction of human cadavers. Segato was born in the Carthusian monastery of Vedana; as a child, Segato learned basic sciences from a Sospirolo priest. After studying under Bagini, Segato spent a short time as an accountant in Treviso before returning to secondary schooling in Belluno, where his teacher was Tomaso Antonio Catullo. From 1818 onwards Segato participated in several archaeological expeditions to Egypt, where he became an expert in the techniques of mummification. Upon his return to Florence in 1823, Segato developed a technique similar to mummification, but unique: rather than removing water from cadavers, Segato's method consisted of what appears to be mineralization or "petrification", his particular technique permitted to save the original colors and features of the textures, besides their elasticity. Most of his works can be found preserved at the University of Florence, but there is an example at the Royal Palace of Caserta: a table in the Old Apartments, the surface of, made with the "petrification" technique.
Word soon spread. Hampered by the society of his time, he was prompted to destroy all his notes before his death. Segato took to the grave the secret of the technique he developed, despite numerous studies and attempts to imitate, remains mysterious, it is said that, on his death, he would reveal his secret to his friend Pellegrini, but he died prematurely. He died in 1836, was buried in the Basilica of Santa Croce. Today, many of Segato's surviving petrified human remains can be found in the Museum of the Department of Anatomy in Florence
Dinosaur Valley State Park
Dinosaur Valley State Park is a state park near Glen Rose, United States. Dinosaur Valley State Park, located just northwest of Glen Rose in Somervell County, is a 1,524.72-acre scenic park set astride the Paluxy River. The land for the park was acquired from private owners under the State Parks Bonds Program during 1968 and opened to the public in 1972. In addition to being a state park, it is a National Natural Landmark. Eastward-dipping limestones and mudstones of the Glen Rose Formation were deposited during the early Cretaceous Period 113 million years ago along the shorelines of an ancient sea, form the geological setting for the park area. Over the last million years or so, these layered formations have been eroded and sculpted by the Paluxy River which, in many places, has cut down to resistant beds and planed off sizable exposures of rock in the river bottom. Near Dinosaur Valley State Park, in the limestone deposits along the Paluxy River, "twin sets" tracks were found in the Glen Rose Formation as early as 1908.
These footprints were once thought to be evidence that humans and non-avian dinosaurs lived at the same time, but now are identified to be created by dinosaurs. However, young-Earth creationists continue to believe that humans and non-avian dinosaurs lived at the same time, a notion, contrary to the standard view of the geological time scale. Biologist Massimo Pigliucci has noted that geologists in the 1980s "clearly demonstrated that no human being left those prints," but rather "they were in fact metatarsal dinosaur tracks, together with a few pure and simple fakes."The family of George Adams, who claimed to have found human footprints in the Glen Rose Formation admitted that Adams' and some others' fossil footprints were a hoax. Zana Douglas, the granddaughter of George Adams, explained that during the 1930s depression her grandfather and other residents of Glen Rose made money by making moonshine and selling "dinosaur fossils"; the faux fossils brought $15 to $30 and when the supply ran low, they "just carved more, some with human footprints thrown in."
Geology Paleontology Trace fossil Sedimentary structures List of Texas state parks Dinosaur Valley State Park, official website A guide to the state park by Glen J. Kuban; the Texas Dinosaur/"Man Track" Controversy by Glen J. Kuban from talk.origins
In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form, resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another. The name means "false form". Terminology for pseudomorphs is "replacer after original", as in brookite after rutile. An infiltration pseudomorph, or substitution pseudomorph is a pseudomorph in which one mineral or other material is replaced by another; the original shape of the mineral remains unchanged, but color and other properties change to those of the replacing mineral. An example of this process is the replacement of wood by silica to form petrified wood in which the substitution may be so perfect as to retain the original cellular structure of the wood. An example of mineral-to-mineral substitution is replacement of aragonite twin crystals by native copper, as occurs at the Corocoro United Copper Mines of Coro Coro, Bolivia. A variety of infiltration or substitution pseudomorphism is called alteration, in which only partial replacement occurs.
This happens when a mineral of one composition changes by chemical reaction to another of similar composition, retaining the original crystalline shape. An example is a change from galena to anglesite; the resulting pseudomorph may contain an unaltered core of galena surrounded by anglesite that has the cubic crystal shape of galena. A paramorph is a mineral changed on the molecular level only, it with a different structure. The mineral looks identical to the original unaltered form; this occurs, in the aragonite to calcite change. An incrustation pseudomorph called epimorph or perimorph, results from a process by which a mineral is coated by another and the encased mineral dissolves; the encasing mineral remains intact, retains the shape of the original mineral or material. Alternatively, another mineral may fill the space occupied by some other mineral or material. Pseudomorphs are common in paleontology. Fossils are formed by pseudomorphic replacement of the remains by mineral matter. Examples pyritized gastropod shells.
In biology, a pseudomorph is a cloud of mucus-rich ink released by many species of cephalopod. The name refers to the similarity in appearance between the cephalopod that released it and the cloud itself, in this context meaning "false body"; this behaviour allows the cephalopod to escape from predation unharmed, is performed as part of what is known as the blanch-ink-jet maneuver. In philosophy, the concept of pseudomorphosis was used by the German philosopher Oswald Spengler to describe the fact that a more powerful civilization can acquire a form belonging to a less powerful civilization. Polymorphism Dana's Manual of Mineralogy by Cornelis S. Hurlbut, Eighteenth Edition, ISBN 0-471-42225-8
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite". Other polymorphs of calcium carbonate are the minerals vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, vaterite is less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime, calx with the suffix -ite used to name minerals, it is thus etymologically related to chalk. When applied by archaeologists and stone trade professionals, the term alabaster is used not just as in geology and mineralogy, where it is reserved for a variety of gypsum. In publications, two different sets of Miller indices are used to describe directions in calcite crystals - the hexagonal system with three indices h, k, l and the rhombohedral system with four indices h, k, l, i. To add to the complications, there are two definitions of unit cell for calcite.
One, an older "morphological" unit cell, was inferred by measuring angles between faces of crystals and looking for the smallest numbers that fit. A "structural" unit cell was determined using X-ray crystallography; the morphological unit cell has approximate dimensions a = 10 Å and c = 8.5 Å, while for the structural unit cell they are a = 5 Å and c = 17 Å. For the same orientation, c must be multiplied by 4 to convert from morphological to structural units; as an example, the cleavage is given as "perfect on " in morphological coordinates and "perfect on " in structural units. Twinning and crystal forms are always given in morphological units. Over 800 forms of calcite crystals have been identified. Most common are scalenohedra, with faces in the hexagonal directions or directions. Habits include acute to tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms, it may occur as fibrous, lamellar, or compact. A fibrous, efflorescent form is known as lublinite.
Cleavage is in three directions parallel to the rhombohedron form. Its fracture is difficult to obtain. Scalenohedral faces are chiral and come in pairs with mirror-image symmetry. Rhombohedral faces are achiral, it has a defining Mohs hardness of 3, a specific gravity of 2.71, its luster is vitreous in crystallized varieties. Color is white or none, though shades of gray, orange, green, violet, brown, or black can occur when the mineral is charged with impurities. Calcite is transparent to opaque and may show phosphorescence or fluorescence. A transparent variety called. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the rhombohedral form is sometimes referred to as "nailhead spar". Single calcite crystals display; this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669. At a wavelength of ≈590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively.
Between 190 and 1700 nm, the ordinary refractive index varies between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, dissolved ion concentrations. Although calcite is insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. When conditions are right for dissolution, the removal of calcite can increase the porosity and permeability of the rock, if it continues for a long period of time may result in the formation of caves.
On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, resulting in various forms of karst topography. Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast, whose name contributed to the term alabaster because of the close association. Many other cultures have used the material for similar carved applications. High-grade optical calcite was used in World War II for gun sights in bomb sights and anti-aircraft weaponry. Experiments have been conducted to use calcite for a cloak of invisibility. Microbiologically precipitated calcite has a wide range of applications, such as soil remediation, soil stabilization and concrete repair. Calcite, obtained from an 80 kg sample of Carrara marble, is used as the IAEA-603 isotopic standard in mass spectrometry for the calibration of δ18O and δ13C. Calcite is a common constituent