Nepheline
Nepheline called nephelite, is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, in their associated pegmatites. Nepheline crystals are rare and belong to the hexagonal system having the form of a short, six-sided prism terminated by the basal plane; the unsymmetrical etched figures produced artificially on the prism faces indicate, that the crystals are hemimorphic and tetartohedral, the only element of symmetry being a polar hexad axis. It is found in compact, granular aggregates, can be white, gray, green, or reddish; the hardness is 5.5 – 6, the specific gravity 2.56 – 2.66. It is translucent with a greasy luster; the low index of refraction and the feeble double refraction in nepheline are nearly the same as in quartz. An important determinative character of nepheline is the ease with which it is decomposed by hydrochloric acid, with separation of gelatinous silica and cubes of salt. For this reason, a clear crystal of nepheline becomes cloudy.
Although sodium and potassium are always present in occurring nepheline in the atomic ratio, artificially prepared crystals have the composition NaAlSiO4. It has therefore been suggested that the orthosilicate formula, AlSiO4, represents the true composition of nepheline; the mineral is one liable to alteration, in the laboratory various substitution products of nepheline have been prepared. In nature it is altered to zeolites, kaolin, or compact muscovite. Gieseckite and liebenerite are pseudomorphs. Two varieties of nepheline are distinguished, differing in their external appearance and in their mode of occurrence, being analogous in these respects to sanidine and common orthoclase respectively. Glassy nepheline has the form of small, transparent crystals and grains with a vitreous luster, it is characteristic of the volcanic rocks rich in alkalis, such as phonolite, nepheline-basalt, leucite basalt, etc. and of certain dike-rocks, such as tinguaite. The best crystals occur with mica, garnet, etc. in the crystal-lined cavities of the ejected blocks of Monte Somma, Vesuvius.
The other variety, known as elaeolite, occurs as large, rough crystals, or more as irregular masses, which have a greasy luster and are opaque, or at most translucent, with a reddish, brownish or grey color. It forms an essential constituent of certain alkaline plutonic rocks of the nepheline syenite series, which are developed in southern Norway; the color and greasy luster of elaeolite are due to the presence of numerous microscopic enclosures of other minerals augite or hornblende. These enclosures sometimes give rise to a chatoyant effect like that of cymophane; this article incorporates text from a publication now in the public domain: Leonard James Spencer. "Nepheline". In Chisholm, Hugh. Encyclopædia Britannica. Cambridge University Press. Media related to Nepheline at Wikimedia Commons
Vug
A vug, vugh, or vugg is a small to medium-sized cavity inside rock. It may be formed through a variety of processes. Most cracks and fissures opened by tectonic activity are filled by quartz and other secondary minerals. Open spaces within ancient collapse breccias are another important source of vugs. Vugs may form when mineral crystals or fossils inside a rock matrix are removed through erosion or dissolution processes, leaving behind irregular voids; the inner surfaces of such vugs are coated with a crystal druse. Fine crystals are found in vugs where the open space allows the free development of external crystal form; the term vug is not applied to veins and fissures that have become filled, but may be applied to any small cavities within such veins. Geodes are a common vug-formed rock, although that term is reserved for more rounded crystal-lined cavities in sedimentary rocks and ancient lavas; the word vug was introduced to the English language by Cornish miners, from the days when Cornwall was a major supplier of tin.
The Cornish word was vooga, which meant "cave". Vesicular texture Rock microstructure Amygdule The dictionary definition of vug at Wiktionary
Density
The density, or more the volumetric mass density, of a substance is its mass per unit volume. The symbol most used for density is ρ, although the Latin letter D can be used. Mathematically, density is defined as mass divided by volume: ρ = m V where ρ is the density, m is the mass, V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials have different densities, density may be relevant to buoyancy and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material water.
Thus a relative density less than one means. The density of a material varies with pressure; this variation is small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid; this causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density. In a well-known but apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated and compared with the mass. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!". As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment; the story first appeared in written form in Vitruvius' books of architecture, two centuries after it took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time. From the equation for density, mass density has units of mass divided by volume; as there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre and the cgs unit of gram per cubic centimetre are the most used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are more practical and US customary units may be used. See below for a list of some of the most common units of density. A number of techniques as well as standards exist for the measurement of density of materials; such techniques include the use of a hydrometer, Hydrostatic balance, immersed body method, air comparison pycnometer, oscillating densitometer, as well as pour and tap. However, each individual method or technique measures different types of density, therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question; the density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is measured with a scale or balance.
To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. If the body is not homogeneous its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ = d m / d V, where d V is an elementary volume at position r; the mass of the body t
Eudialyte
Eudialyte, whose name derives from the Greek phrase Εὖ διάλυτος eu dialytos, meaning "well decomposable", is a somewhat rare, nine member ring cyclosilicate mineral, which forms in alkaline igneous rocks, such as nepheline syenites. Its name alludes to its ready solubility in acid. Eudialyte was first described in 1819 for an occurrence in nepheline syenite of the Ilimaussaq intrusive complex of southwest Greenland. Eudialyte is used as a minor ore of zirconium. Another use of eudialyte is as a minor gemstone, but this use is limited by its rarity, compounded by its poor crystal habit; these factors make eudialyte of primary interest as a collector's mineral. Eudialyte has a significant content of U, Pb, Nb, Ta, Zr, Hf, rare earth elements; because of this, geoscientists use eudialyte as a geochronometer to date and investigate the genesis of the host rocks. Eudialyte is found associated with other alkalic igneous minerals, in addition to some minerals common to most igneous material in general.
Associate minerals include: microcline, aegirine, lorenzenite, murmanite, sodalite, rinkite, låvenite and titanian magnetite. Alternative names of eudialyte include: almandine spar, Saami blood. Eucolite is the name of an optically negative variety, more the group member: ferrokentbrooksite. Eudialyte's rarity makes locality useful in its identification. Prominent localities of eudialyte include Mont Saint-Hilaire in Canada, Kola Peninsula in Russia and Poços de Caldas in Brazil, but it is found in Greenland and Arkansas; the lack of crystal habit, associated with color, is useful for identification, as are associated minerals. A pink-red mineral with no good crystals associated with other alkaline igneous material nepheline and aegirine, is a good indication a specimen is eudialyte. Microchemical and structural analyses of different eudialyte samples have revealed the presence of many new eudialyte-like minerals; these minerals joined into the eudialyte group. The group includes Zr-, OH-, Cl-, F-, CO3- and also SO4-bearing silicates of Na, K, H3O, Ca, Sr, REEs, Mn, Fe, Nb and W. Electron vacancies can be present in their structure, too.
Mineral Galleries Johnsen, O.. A.. G.. R.. V.. "The nomenclature of eudialyte-group minerals". The Canadian Mineralogist. 41: 785–794. Doi:10.2113/gscanmin.41.3.785
Lustre (mineralogy)
Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux, meaning "light", implies radiance, gloss, or brilliance. A range of terms are used to describe lustre, such as earthy, metallic and silky; the term vitreous refers to a glassy lustre. A list of these terms is given below. Lustre varies over a wide continuum, so there are no rigid boundaries between the different types of lustre; the terms are combined to describe intermediate types of lustre. Some minerals exhibit unusual optical phenomena, such as asterism or chatoyancy. A list of such phenomena is given below. Adamantine minerals possess a superlative lustre, most notably seen in diamond; such minerals are transparent or translucent, have a high refractive index. Minerals with a true adamantine lustre are uncommon, with examples being cerussite and cubic zirconia. Minerals with a lesser degree of lustre are referred to as subadamantine, with some examples being garnet and corundum.
Dull minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, approximating a Lambertian reflector. An example is kaolinite. A distinction is sometimes drawn between dull minerals and earthy minerals, with the latter being coarser, having less lustre. Greasy minerals resemble grease. A greasy lustre occurs in minerals containing a great abundance of microscopic inclusions, with examples including opal and cordierite, jadeite. Many minerals with a greasy lustre feel greasy to the touch. Metallic minerals have the lustre of polished metal, with ideal surfaces will work as a reflective surface. Examples include galena and magnetite. Pearly minerals consist of thin transparent co-planar sheets. Light reflecting from these layers give them a lustre reminiscent of pearls; such minerals possess perfect cleavage, with examples including stilbite. Resinous minerals have the appearance of chewing gum or plastic. A principal example is amber, a form of fossilized resin.
Silky minerals have a parallel arrangement of fine fibres, giving them a lustre reminiscent of silk. Examples include asbestos and the satin spar variety of gypsum. A fibrous lustre has a coarser texture. Submetallic minerals are duller and less reflective. A submetallic lustre occurs in near-opaque minerals with high refractive indices, such as sphalerite and cuprite. Vitreous minerals have the lustre of glass; this type of lustre is one of the most seen, occurs in transparent or translucent minerals with low refractive indices. Common examples include calcite, topaz, beryl and fluorite, among others. Waxy minerals have a lustre resembling wax. Examples include chalcedony. Asterism is the display of a star-shaped luminous area, it is seen in some rubies, where it is caused by impurities of rutile. It can occur in garnet and spinel. Aventurescence is a reflectance effect like that of glitter, it arises from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they influence the material's body colour.
In aventurine quartz, chrome-bearing fuchsite makes for a green stone and various iron oxides make for a red stone. Chatoyant minerals display luminous bands; such minerals are composed of parallel fibers, which reflect light into a direction perpendicular to their orientation, thus forming narrow bands of light. The most famous examples are tiger's eye and cymophane, but the effect may occur in other minerals such as aquamarine and tourmaline. Color change is most found in alexandrite, a variety of chrysoberyl gemstones. Other gems occur in color-change varieties, including sapphire, spinel. Alexandrite displays a color change dependent upon light, along with strong pleochroism; the gem results from small-scale replacement of aluminium by chromium oxide, responsible for alexandrite's characteristic green to red color change. Alexandrite from the Ural Mountains in Russia is green by red by incandescent light. Other varieties of alexandrite may be yellowish or pink in daylight and a columbine or raspberry red by incandescent light.
The optimum or "ideal" color change would be fine emerald green to fine purplish red, but this is rare. Iridescence is the'play' or'fire' of rainbow-coloured light caused by thin regular structures or layers beneath the surface of a gemstone. Similar to a thin film of oil on water, these layers interfere with the rays of reflected light, reinforcing some colours and cancelling others. Iridescence is seen at its best in precious opal. Schiller, from German for "color play", is the metallic iridescence originating from below the surface of a stone that occurs when light is reflected between layers of minerals, it is seen in moonstone and labradorite and is similar to adularescence and aventurescence
Mont Saint-Hilaire
Mont Saint-Hilaire, is an isolated hill, 414 m high, in the Montérégie region of southern Quebec. It is about thirty kilometres east of Montreal, east of the Richelieu River, it is one of the Monteregian Hills. Around the mountains are the towns of Mont-Saint-Hilaire and Saint-Jean-Baptiste. Other nearby towns include Otterburn Beloeil and McMasterville; the area surrounding the mountain is a biosphere reserve, as one of the last remnants of the primeval forests of the Saint-Lawrence valley. Most of the mountain is the property of McGill University, as the Gault Nature Reserve, considered the third McGill campus; the University has opened the western half of the mountain to visitors for hiking and cross-country skiing, as the Milieu Naturel. The eastern half, or Milieu de Conservation is not accessible to the general public; until the late nineteenth century, the lack of information on more remote summits of Quebec, as well as the high prominence of Mont Saint-Hilaire, led to it being mistaken as the highest summit in Québec.
In actuality, Saint-Hilaire's 414 metres falls far short of making it the highest mountain in Quebec. Mont Saint-Hilaire is home to a wide variety of fauna and flora, as well as a number of rare minerals, including some which were discovered on the mountain and some which are unique to the region; these minerals are exploited by a quarry on the north-eastern side of the mountain. In addition, the soil is ideal for the growth of apple trees, the mountain's apple orchards draws tens of thousands of visitors each year; the mountain stands 400 metres above the surrounding plains. It has several summits, surrounding Lac Hertel. Most of the well-known summits of the mountain are in the western part, they are the Pain de Sucre, 414 m high, the Sunrise, 405 m high, the Rocky, 403 m high, the Sommet Dieppe, 371 m high as well as Burnt Hill. The summits of the eastern half of the mountain, closed to the public, are little known, to the point that most official maps fail to identify the distinct summits at all.
Only a few names are known, such as Lake Hill. These summits range from 277 to 392 metres in elevation; the best-known feature of the mountain is the cliffs. Collectively known as the falaise dieppe, or falaise de Dieppe the cliffs are part of the Dieppe summit, nearly 175 m high; some of the best known features of the cliffs include the 60-metre high Tour rouge, as well as two slabs, the Dalle noire and Dalle Verte, which rise at a 75-degree angle. The cliff's unique ecosystem hosts lichens, as well as cedar trees, some of which may be as much as five hundred years old, it hosts the mountain's population of peregrine falcons. However, the action of rock climbers has proven destructive to the ecosystem, in addition to being dangerous to the climbers themselves. A white cross on the cliff commemorates the death of a boy scout in 1941. At the centre of the mountain is Lac Hertel, a lake in a glacially-formed depression in the middle of the various summits, it covers an area of 0.3 square kilometre, has a maximum depth of 9 m.
It is fed by three permanent streams. The lake serves as a secondary reservoir of drinking water to the region, and, as such, swimming and boating are forbidden; the central position of the lake on the mountain has led to claims that Mont Saint-Hilaire is a volcanic caldera. However, the lake is the result of glacial erosion, in no way an ancient volcanic crater. Mont Saint-Hilaire is one of the Monteregian Hills, a group of erosional remnants of intrusive mountains spread across southern Quebec, it is composed of three distinct plutonic intrusions that formed during the Cretaceous Period between 133 and 120 million years ago. Like the other Monteregian Hills, Mont Saint-Hilaire forms part of the Great Meteor hotspot track, created when the North American Plate slid over the New England hotspot. During this time, melting occurred. Erosion of the surrounding softer sedimentary rocks revealed the more resistant rocks of Mont Saint-Hilaire. Mont Saint-Hilaire is a famous mineral locality because of its great number of rare and exotic mineral species.
Annite from Mont Saint-Hilaire is among the most iron-rich found in nature. In the gabbro, biotite has lower manganese content, but is titanium-rich. Phlogopite is found as small metamorphic crystals in marble xenoliths within the syenite. Siderophyllite, a rare mineral, occurs as large crystals in a metasomatised albite-rich albitite dike. In addition to gabbro, the second intrusive suite included nepheline syenite and monzonite; the third intrusive occupies the eastern side and is peralkaline nepheline syenites and porphyrites. The most mineralogically interesting are the associated agpaitic pegmatites, the intrusive breccias, the hornfels derived from the metasomatised sedimentary wall rocks. There have been over 366 distinct species of minerals collected at Mont Saint-Hilaire, 50 of which have this site as type locality; as the last remnant in Quebec of the ancient Gulf of St. Lawrence lowland forests, the area has been a provincial biosphere reserve since 1978 and a federal Migratory Bi
Silicate minerals
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up 90 percent of the Earth's crust. In mineralogy, silica SiO2 is considered a silicate mineral. Silica is found in nature as the mineral quartz, its polymorphs. On Earth, a wide variety of silicate minerals occur in an wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years; these processes include partial melting, fractionation, metamorphism and diagenesis. Living organisms contribute to this geologic cycle. For example, a type of plankton known as diatoms construct their exoskeletons from silica extracted from seawater; the tests of dead diatoms are a major constituent of deep ocean sediment, of diatomaceous earth. A silicate mineral is an ionic compound whose anions consist predominantly of silicon and oxygen atoms. In most minerals in the Earth's crust, each silicon atom is the center of an ideal tetrahedron, whose corners are four oxygen atoms covalently bound to it.
Two adjacent tetrahedra may share a vertex, meaning that the oxygen atom is a bridge connecting the two silicon atoms. An unpaired vertex represents an ionized oxygen atom, covalently bound to a single silicon atom, that contributes one unit of negative charge to the anion; some silicon centers may be replaced by atoms of other elements, still bound to the four corner oxygen corners. If the substituted atom is not tetravalent, it contributes extra charge to the anion, which requires extra cations. For example, in the mineral orthoclase n, the anion is a tridimensional network of tetrahedra in which all oxygen corners are shared. If all tetrahedra had silicon centers, the anion would be just neutral silica n. Replacement of one every four silicon atoms by an aluminum atom results in the anion n, whose charge is neutralized by the potassium cations K+. In mineralogy, silicate minerals are classified into seven major groups according to the structure of their silicate anion: Note that tectosilicates can only have additional cations if some of the silicon is replaced by an atom of lower valence such as aluminium.
Al for Si substitution is common. Nesosilicates, or orthosilicates, have the orthosilicate ion, which constitute isolated 4− tetrahedra that are connected only by interstitial cations; the Nickel–Strunz classification is 09. A –examples include: Phenakite group Phenakite – Be2SiO4 Willemite – Zn2SiO4 Olivine group Forsterite – Mg2SiO4 Fayalite – Fe2SiO4 Tephroite – Mn2SiO4 Garnet group Pyrope – Mg3Al23 Almandine – Fe3Al23 Spessartine – Mn3Al23 Grossular – Ca3Al23 Andradite – Ca3Fe23 Uvarovite – Ca3Cr23 Hydrogrossular – Ca3Al2Si2O83−m4m Zircon group Zircon – ZrSiO4 Thorite – SiO4 Hafnon – SiO4 Al2SiO5 group Andalusite – Al2SiO5 Kyanite – Al2SiO5 Sillimanite – Al2SiO5 Dumortierite – Al6.5–7BO333 Topaz – Al2SiO42 Staurolite – Fe2Al942 Humite group – 732Norbergite – Mg32 Chondrodite – Mg522 Humite – Mg732 Clinohumite – Mg942 Datolite – CaBSiO4 Titanite – CaTiSiO5 Chloritoid – 2Al4Si2O104 Mullite – Al6Si2O13 Sorosilicates have isolated pyrosilicate anions Si2O6−7, consisting of double tetrahedra with a shared oxygen vertex—a silicon:oxygen ratio of 2:7.
The Nickel–Strunz classification is 09. B. Examples include: Hemimorphite – Zn42·H2O Lawsonite – CaAl22·H2O Axinite – 3Al2 Ilvaite – CaFeII2FeIIIO Epidote group Epidote – Ca23O Zoisite – Ca2Al3O Tanzanite – Ca2Al3O Clinozoisite – Ca2Al3O Allanite – CaAl2O Dollaseite- – CaCeMg2AlSi3O11F Vesuvianite – Ca102Al4524 Cyclosilicates, or ring silicates, have three or more tetrahedra linked in a ring; the general formula is 2x−, where one or more silicon atoms can be replaced by other 4-coordinated atom. The silicon:oxygen ratio is 1:3. Double rings have the formula 2x−; the Nickel–Strunz classification is 09. C. Possible ring sizes include: Some example minerals are: 3-member single ring Benitoite – BaTi 4-member single ring Papagoite – CaCuAlSi2O63. 6-member single ring Beryl – Be3Al2 Bazzite – Be3Sc2 Sugilite – KNa22Li3Si12O30 Tourmaline – 3−634 Pezzottaite – CsAl2Si6O18 Osumilite – 2312O30 Cordierite – 2Al4Si5O18 Sekaninaite – 2Al4Si5O18 9-member single ring Eudialyte – Na15Ca63Zr3SiO3222 6-member double ring Milarite – K2Ca4Al2Be4H2ONote that the ring in axinite contains two B and four Si tetrahedra and is distorted compared to the other 6-member ring cyclosilicates.
Inosilicates, or chain silicates, have interlocking chains of silicate tetrahedra with either SiO3, 1:3 ratio, for single chains or Si4O11, 4:11 ratio, for double chains. The Nickel–Strunz classification is 09. D – examples include: Pyroxene group Enstatite – orthoferrosilite series Enstatite – MgSiO3 Ferrosilite – FeSiO3 Pigeonite – Ca0.251.75Si2O6 Diopside – hedenbergite series Diopside – CaMgSi2O6 Hedenbergite – CaFeSi2O6 Augite – 2O6 Sodium pyroxene series Jadeite – NaAlSi2O6 Aegirine (or ac
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