Fracture (mineralogy)
In the field of mineralogy, fracture is the texture and shape of a rock's surface formed when a mineral is fractured. Minerals have a distinctive fracture, making it a principal feature used in their identification. Fracture differs from cleavage in that the latter involves clean splitting along the cleavage planes of the mineral's crystal structure, as opposed to more general breakage. All minerals exhibit fracture, but when strong cleavage is present, it can be difficult to see. Conchoidal fracture breakage that resembles the concentric ripples of a mussel shell, it occurs in amorphous or fine-grained minerals such as flint, opal or obsidian, but may occur in crystalline minerals such as quartz. Subconchoidal fracture is similar to with less significant curvature. Earthy fracture is reminiscent of freshly broken soil, it is seen in soft, loosely bound minerals, such as limonite and aluminite. Hackly fracture is jagged and not even, it occurs when metals are torn, so is encountered in native metals such as copper and silver.
Splintery fracture comprises sharp elongated points. It is seen in fibrous minerals such as chrysotile, but may occur in non-fibrous minerals such as kyanite. Uneven fracture is a rough one with random irregularities, it occurs in a wide range of minerals including arsenopyrite and magnetite. Rudolf Duda and Lubos Rejl: Minerals of the World http://www.galleries.com/minerals/property/fracture.htm
Sri Lanka
Sri Lanka the Democratic Socialist Republic of Sri Lanka, is an island country in South Asia, located in the Indian Ocean to the southwest of the Bay of Bengal and to the southeast of the Arabian Sea. The island is geographically separated from the Indian subcontinent by the Gulf of Mannar and the Palk Strait; the legislative capital, Sri Jayawardenepura Kotte, is a suburb of the commercial capital and largest city, Colombo. Sri Lanka's documented history spans 3,000 years, with evidence of pre-historic human settlements dating back to at least 125,000 years, it has a rich cultural heritage and the first known Buddhist writings of Sri Lanka, the Pāli Canon, date back to the Fourth Buddhist council in 29 BC. Its geographic location and deep harbours made it of great strategic importance from the time of the ancient Silk Road through to the modern Maritime Silk Road. Sri Lanka was known from the beginning of British colonial rule as Ceylon. A nationalist political movement arose in the country in the early 20th century to obtain political independence, granted in 1948.
Sri Lanka's recent history has been marred by a 26-year civil war, which decisively ended when the Sri Lanka Armed Forces defeated the Liberation Tigers of Tamil Eelam in 2009. The current constitution stipulates the political system as a republic and a unitary state governed by a semi-presidential system, it has had a long history of international engagement, as a founding member of the South Asian Association for Regional Cooperation, a member of the United Nations, the Commonwealth of Nations, the G77, the Non-Aligned Movement. Along with the Maldives, Sri Lanka is one of only two South Asian countries rated "high" on the Human Development Index, with its HDI rating and per capita income the highest among South Asian nations; the Sri Lankan constitution accords Buddhism the "foremost place", although it does not identify it as a state religion. Buddhism is given special privileges in the Sri Lankan constitution; the island is home to many cultures and ethnicities. The majority of the population is from the Sinhalese ethnicity, while a large minority of Tamils have played an influential role in the island's history.
Moors, Malays and the indigenous Vedda are established groups on the island. In antiquity, Sri Lanka was known to travellers by a variety of names. According to the Mahavamsa, the legendary Prince Vijaya named the land Tambapanni, because his followers' hands were reddened by the red soil of the area. In Hindu mythology, such as the Ramayana, the island was referred to as Lankā; the Tamil term Eelam, was used to designate the whole island in Sangam literature. The island was known under Chola rule as Mummudi Cholamandalam. Ancient Greek geographers called it Taprobanē from the word Tambapanni; the Persians and Arabs referred to it as Sarandīb from Cerentivu or Siṃhaladvīpaḥ. Ceilão, the name given to Sri Lanka by the Portuguese Empire when it arrived in 1505, was transliterated into English as Ceylon; as a British crown colony, the island was known as Ceylon. The country is now known in Sinhala in Tamil as Ilaṅkai. In 1972, its formal name was changed to "Free and Independent Republic of Sri Lanka".
In 1978 it was changed to the "Democratic Socialist Republic of Sri Lanka". As the name Ceylon still appears in the names of a number of organisations, the Sri Lankan government announced in 2011 a plan to rename all those over which it has authority; the pre-history of Sri Lanka goes back 125,000 years and even as far back as 500,000 years. The era spans the Palaeolithic and early Iron Ages. Among the Paleolithic human settlements discovered in Sri Lanka, which dates back to 37,000 BP, Batadombalena and Belilena are the most important. In these caves, archaeologists have found the remains of anatomically modern humans which they have named Balangoda Man, other evidence suggesting that they may have engaged in agriculture and kept domestic dogs for driving game. One of the first written references to the island is found in the Indian epic Ramayana, which provides details of a kingdom named Lanka, created by the divine sculptor Vishwakarma for Kubera, the Lord of Wealth, it is said that Kubera was overthrown by his demon stepbrother Ravana, the powerful emperor who built a mythical flying machine named Dandu Monara.
The modern city of Wariyapola is described as Ravana's airport. Early inhabitants of Sri Lanka were ancestors of the Vedda people, an indigenous people numbering 2,500 living in modern-day Sri Lanka; the 19th-century Irish historian James Emerson Tennent theorized that Galle, a city in southern Sri Lanka, was the ancient seaport of Tarshish from which King Solomon is said to have drawn ivory and other valuables. According to the Mahāvamsa, a chronicle written in Pāḷi, the original inhabitants of Sri Lanka are the Yakshas and Nagas. Ancient cemeteries that were used before 600 BC and other signs of advanced civilisation have been discovered in Sri Lanka. Sinhalese history traditionally starts in 543 BC with the arrival of Prince Vijaya, a semi-legendary prince who sailed with 700 followers to Sri Lanka, after being expelled from Vanga Kingdom (present-day Ben
Crystal habit
In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. A single crystal's habit is a description of its general shape and its crystallographic forms, plus how well developed each form is. Recognizing the habit may help in identifying a mineral; when the faces are well-developed due to uncrowded growth a crystal is called euhedral, one with developed faces is subhedral, one with undeveloped crystal faces is called anhedral. The long axis of a euhedral quartz crystal has a six-sided prismatic habit with parallel opposite faces. Aggregates can be formed of individual crystals with euhedral to anhedral grains; the arrangement of crystals within the aggregate can be characteristic of certain minerals. For example, minerals used for asbestos insulation grow in a fibrous habit, a mass of fine fibers; the terms used by mineralogists to report crystal habits describe the typical appearance of an ideal mineral. Recognizing the habit can aid in identification as some habits are characteristic.
Most minerals, however, do not display ideal habits due to conditions during crystallization. Euhedral crystals formed in uncrowded conditions with no adjacent crystal grains are not common. Factors influencing habit include: a combination of two or more crystal forms. Minerals belonging to the same crystal system do not exhibit the same habit; some habits of a mineral are unique to its variety and locality: For example, while most sapphires form elongate barrel-shaped crystals, those found in Montana form stout tabular crystals. Ordinarily, the latter habit is seen only in ruby. Sapphire and ruby are both varieties of the same mineral: corundum; some minerals may replace other existing minerals while preserving the original's habit: this process is called pseudomorphous replacement. A classic example is tiger's eye quartz, crocidolite asbestos replaced by silica. While quartz forms prismatic crystals, in tiger's eye the original fibrous habit of crocidolite is preserved; the names of crystal habits are derived from: Predominant crystal faces.
Crystal forms. Aggregation of crystals or aggregates. Crystal appearance. Abnormal grain growth Grain growth
Benjamin Silliman
Benjamin Silliman was an early American chemist and science educator. He was one of the first American professors of science, at Yale College, the first person to distill petroleum in America, a founder of the American Journal of Science, the oldest continuously published scientific journal in the United States. Silliman was born in a tavern in North Stratford, now Trumbull, Connecticut, a few months after his mother, Mary Silliman, fled for her life from their Fairfield, home to escape two thousand invading British troops that burned Fairfield center to the ground; the British forces had taken his father, General Gold Selleck Silliman, prisoner in May 1779. Silliman was educated at Yale, receiving a B. A. degree in 1796 and a M. A. in 1799. He studied law with Simeon Baldwin from 1798 to 1799 and became a tutor at Yale from 1799 to 1802, he was admitted to the bar in 1802. That same year he was hired by Yale President Timothy Dwight IV as a professor of chemistry and natural history despite his never having studied chemistry.
To prepare for this new position, Silliman studied chemistry with Professor James Woodhouse at the University of Pennsylvania in Philadelphia and delivered his first lectures in chemistry at Yale in 1804. These lectures were the first science lectures given at Yale. In 1805, he traveled to Edinburgh for further study. Returning to New Haven, he studied its geology, made a chemical analysis of the meteorite that fell near Weston, publishing the first scientific account of any American meteorite, he lectured publicly at New Haven in 1808 and came to discover many of the constituent elements of many minerals. Some time around 1818, Ephraim Lane took some samples of rocks he found at an area called Saganawamps, now a part of the Old Mine Park Archeological Site in Trumbull, Connecticut, to Silliman for identification. Silliman reported in his new American Journal of Science, a publication covering all the natural sciences but with an emphasis on geology, that he had identified tungsten, tellurium and fluorite in the rocks.
He played. In 1837, the first prismatic barite ore of tungsten in the United States was discovered at the mine; the mineral sillimanite was named after Silliman in 1850. Upon the founding of the Medical School, he taught there as one of the founding faculty members. In 1833 he discussed the relationship of Flood geology to the Genesis account, wrote about this topic in 1840. Silliman was an early supporter of coeducation in the Ivy League. Although Yale wouldn't admit women as students until over 100 years he allowed young women into his lecture classes, his efforts convinced Frederick Barnard President of Columbia College, that women ought to be admitted as students. "The elder Silliman, during the entire period of his distinguished career as a Professor of Chemistry and Mineralogy in Yale College, was accustomed every year to admit to his lecture-courses classes of young women from the schools of New Haven. In that institution the undersigned had an opportunity to observe, as a student, the effect of the practice, similar to that which he afterward created for himself in Alabama, as a teacher.
The results in both instances, so far, were good. McCullough relates that Silliman would become president of the college; as professor emeritus, he delivered lectures at Yale on geology until 1855. Like his son-in-law James Dana, Silliman was a Christian. In an address delivered before the Association of American Geologists he spoke in favor of old-earth creationism, stating: It is admitted by multitudes, that the chronology of the Scriptures is, in strictness, applied only to the history of our race, the sole moral beings whom God has placed in this World. In the same line of thought, he posed arguments against materialism. At 6:30 in the morning of December 14, 1807, a blazing fireball about two-thirds the size of the moon, was seen traveling southwards by early risers in Vermont and Massachusetts. Three loud explosions were heard over the town of Weston in Connecticut. Stone fragments fell in at least 6 places; the largest and only unbroken stone of the Weston fall, which weighed 36.5 pounds, was found some days after Silliman and Kingsley had spent several fruitless hours hunting for it.
The owner, a Trumbull farmer named Elijah Seeley, was urged to present it to Yale by local people who had met the professors during their investigation, but he insisted on putting it up for sale. It was purchased by Colonel George Gibbs for his famous collection of minerals, his first marriage
Cordierite
"Praseolite" redirects here. For the green variety of quartz see prasiolite. Cordierite or iolite is a magnesium iron aluminium cyclosilicate. Iron is always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: 2Al3 to 2Al3. A high-temperature polymorph exists, isostructural with beryl and has a random distribution of Al in the 6O18 rings. Cordierite, discovered in 1813, in specimens from Níjar, Almería is named after the French geologist Louis Cordier. Cordierite occurs in contact or regional metamorphism of pelitic rocks, it is common in hornfels produced by contact metamorphism of pelitic rocks. Two common metamorphic mineral assemblages include sillimanite-cordierite-spinel and cordierite-spinel-plagioclase-orthopyroxene. Other associated minerals include anthophyllite. Cordierite occurs in some granites and norites in gabbroic magmas. Alteration products include mica and talc. Cordierite occurs, in the granite contact zone at Geevor Tin Mine in Cornwall.
Catalytic converters are made from ceramics containing a large proportion of synthetic cordierite. The manufacturing process deliberately aligns the cordierite crystals to make use of the low thermal expansion along one axis; this prevents thermal shock cracking from taking place. As the transparent variety iolite, it is used as a gemstone; the name "iolite" comes from the Greek word for violet. Another old name is dichroite, a Greek word meaning "two-colored rock", a reference to cordierite's strong pleochroism, it has been called "water-sapphire" and "Vikings' Compass" because of its usefulness in determining the direction of the sun on overcast days, the Vikings having used it for this purpose. This works by determining the direction of polarization of the sky overhead. Light scattered by air molecules is polarized, the direction of the polarization is at right angles to a line to the sun when the sun's disk itself is obscured by dense fog or lies just below the horizon. Gem quality iolite varies in color from sapphire blue to blue violet to yellowish gray to light blue as the light angle changes.
Iolite is sometimes used as an inexpensive substitute for sapphire. It is much softer than sapphires and is abundantly found in Australia, Burma, India, Namibia, Sri Lanka and the United States; the largest iolite crystal found weighed more than 24,000 carats, was discovered in Wyoming, US. Another name for blue iolite is steinheilite, after Fabian Steinheil, the Russian military governor of Finland who observed that it was a different mineral from quartz. Praseolite is another iolite variety, it should not be confused with prasiolite. List of minerals List of minerals named after people Sunstone Mineral galleries http://www.gemstone.org/gem-by-gem/english/iolite.html
Mohs scale of mineral hardness
The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, some of which are more quantitative; the method of comparing hardness by observing which minerals can scratch others is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c. 300 BC, followed by Pliny the Elder in his Naturalis Historia, c. 77 AD. While facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Despite its lack of precision, the Mohs scale is relevant for field geologists, who use the scale to identify minerals using scratch kits; the Mohs scale hardness of minerals can be found in reference sheets. Mohs hardness is useful in milling, it allows assessment of.
The scale is used at electronic manufacturers for testing the resilience of flat panel display components. The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly; the samples of matter used by Mohs are all different minerals. Minerals are chemically pure solids found in nature. Rocks are made up of one or more minerals; as the hardest known occurring substance when the scale was designed, diamonds are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5. "Scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number.
While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number. The Mohs scale is a purely ordinal scale. For example, corundum is twice as hard as topaz; the table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples. On the Mohs scale, a streak plate has a hardness of 7.0. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale; the table below incorporates additional substances that may fall between levels: Comparison between hardness and hardness: Mohs hardness of elements is taken from G. V. Samsonov in Handbook of the physicochemical properties of the elements, IFI-Plenum, New York, USA, 1968. Cordua, William S. "The Hardness of Minerals and Rocks". Lapidary Digest, c. 1990
Gneiss
Gneiss is a common and distributed type of metamorphic rock. Gneiss is formed by high temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Orthogneiss is gneiss derived from igneous rock. Paragneiss is gneiss derived from sedimentary rock. Gneiss forms at higher pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct foliation; the word gneiss has been used in English since at least 1757. It is borrowed from the German word Gneis also spelled Gneiss, derived from the Middle High German noun gneist "spark". Gneiss is formed from sedimentary or igneous rock exposed to temperatures greater than 320°C and high pressure. Gneissic rocks are medium- to coarse-foliated. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc. Gneiss rocks may be named after a characteristic component such as garnet gneiss, biotite gneiss, albite gneiss, etc.
Orthogneiss designates a gneiss derived from an igneous rock, paragneiss is one from a sedimentary rock. Gneissose rocks have properties similar to gneiss. Gneiss appears to be striped in bands like parallel lines in shape, called gneissic banding; the banding is developed under high pressure conditions. The minerals are arranged into layers; the appearance of layers, called'compositional banding', occurs because the layers, or bands, are of different composition. The darker bands have more mafic minerals; the lighter bands contain more felsic minerals. A common cause of the banding is the subjection of the protolith to extreme shearing force, a sliding force similar to the pushing of the top of a deck of cards in one direction, the bottom of the deck in the other direction; these forces stretch out the rock like a plastic, the original material is spread out into sheets. Some banding is formed from original rock material, subjected to extreme temperature and pressure and is composed of alternating layers of sandstone and shale, metamorphosed into bands of quartzite and mica.
Another cause of banding is "metamorphic differentiation", which separates different materials into different layers through chemical reactions, a process not understood. Not all gneiss rocks have detectable banding. In kyanite gneiss, crystals of kyanite appear as random clumps in what is a plagioclase matrix. Augen gneiss, from the German: Augen, meaning "eyes", is a coarse-grained gneiss resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear-bound feldspar porphyroclasts microcline, within the layering of the quartz and magnetite bands. Henderson gneiss is found in South Carolina, US, east of the Brevard Shear Zone, it has deformed into two sequential forms. The second, more warped, form is associated with the Brevard Fault, the first deformation results from displacement to the southwest. Most of the Outer Hebrides of Scotland have a bedrock formed from Lewisian gneiss. In addition to the Outer Hebrides, they form basement deposits on the Scottish mainland west of the Moine Thrust and on the islands of Coll and Tiree.
These rocks are igneous in origin, mixed with metamorphosed marble and mica schist with intrusions of basaltic dikes and granite magma. Gneisses of Archean and Proterozoic age occur in the Baltic Shield. List of rock types Blatt and Robert J. Tracy. Petrology: Igneous and Metamorphic, 2nd ed. Freeman, pp. 359–65. ISBN 0-7167-2438-3. Gillen, Con. Geology and landscapes of Scotland. Harpenden. Terra Publishing. ISBN 1-903544-09-2. Harper, Douglas. "gneiss", Online Etymological Dictionary. Retrieved 2015-03-01. Marshak, Stephen. Essentials of Geology. W. W. Norton. ISBN 978-0-393-91939-4. McKirdy, Roger Crofts and John Gordon. Land of Mountain and Flood: The Geology and Landforms of Scotland. Edinburgh. Birlinn. ISBN 978-1-84158-357-0. Murray, W. H.. The Hebrides. London. Heinemann. Sacks, Paul E. and Donald T. Secor. "Kinematics of Late Paleozoic continental collision between Laurentia and Gondwana". Science, 250: 1702–05. Doi:10.1126/science.250.4988.1702. "Gneiss". Encyclopædia Britannica. 1911. "Gneiss". New International Encyclopedia.
1906
