Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. Cleavage forms parallel to planes, Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Mica has basal cleavage, this is why mica can be peeled into thin sheets, cubic cleavage occurs on when there are three cleavage planes intersecting at 90 degrees. Halite has cubic cleavage, and therefore, when halite crystals are broken, octahedral cleavage occurs when there are four cleavage planes in a crystal. Octahedral cleavage is common for semiconductors, rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Prismatic cleavage occurs when there are two planes in a crystal. Dodecahedral cleavage occurs when there are six cleavage planes in a crystal, crystal parting occurs when minerals break along planes of structural weakness due to external stress or along twin composition planes. Parting breaks are very similar in appearance to cleavage, but only due to stress.
Examples include magnetite which shows octahedral parting, the parting of corundum. Cleavage is a property traditionally used in mineral identification, both in hand specimen and microscopic examination of rock and mineral studies. As an example, the angles between the cleavage planes for the pyroxenes and the amphiboles are diagnostic. Crystal cleavage is of importance in the electronics industry and in the cutting of gemstones. Precious stones are generally cleaved by impact, as in diamond cutting, synthetic single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave. Elemental semiconductors are diamond cubic, a group for which octahedral cleavage is observed. This means that some orientations of wafer allow near-perfect rectangles to be cleaved, most other commercial semiconductors can be made in the related zinc blende structure, with similar cleavage planes. Cleavage Mineral galleries, Mineral properties – Cleavage
Poland, officially the Republic of Poland, is a country in Central Europe, situated between the Baltic Sea in the north and two mountain ranges in the south. Bordered by Germany to the west, the Czech Republic and Slovakia to the south and Belarus to the east, the total area of Poland is 312,679 square kilometres, making it the 69th largest country in the world and the 9th largest in Europe. With a population of over 38.5 million people, Poland is the 34th most populous country in the world, the 8th most populous country in Europe, Poland is a unitary state divided into 16 administrative subdivisions, and its capital and largest city is Warsaw. Other metropolises include Kraków, Wrocław, Poznań, Gdańsk and Szczecin, the establishment of a Polish state can be traced back to 966, when Mieszko I, ruler of a territory roughly coextensive with that of present-day Poland, converted to Christianity. The Kingdom of Poland was founded in 1025, and in 1569 it cemented a political association with the Grand Duchy of Lithuania by signing the Union of Lublin.
This union formed the Polish–Lithuanian Commonwealth, one of the largest and most populous countries of 16th and 17th century Europe, Poland regained its independence in 1918 at the end of World War I, reconstituting much of its historical territory as the Second Polish Republic. In September 1939, World War II started with the invasion of Poland by Nazi Germany, followed thereafter by invasion by the Soviet Union. More than six million Polish citizens died in the war, after the war, Polands borders were shifted westwards under the terms of the Potsdam Conference. With the backing of the Soviet Union, a communist puppet government was formed, and after a referendum in 1946. During the Revolutions of 1989 Polands Communist government was overthrown and Poland adopted a new constitution establishing itself as a democracy, informally called the Third Polish Republic. Since the early 1990s, when the transition to a primarily market-based economy began, Poland has achieved a high ranking on the Human Development Index.
Poland is a country, which was categorised by the World Bank as having a high-income economy. Furthermore, it is visited by approximately 16 million tourists every year, Poland is the eighth largest economy in the European Union and was the 6th fastest growing economy on the continent between 2010 and 2015. According to the Global Peace Index for 2014, Poland is ranked 19th in the list of the safest countries in the world to live in. The origin of the name Poland derives from a West Slavic tribe of Polans that inhabited the Warta River basin of the historic Greater Poland region in the 8th century, the origin of the name Polanie itself derives from the western Slavic word pole. In some foreign languages such as Hungarian, Lithuanian and Turkish the exonym for Poland is Lechites, historians have postulated that throughout Late Antiquity, many distinct ethnic groups populated the regions of what is now Poland. The most famous archaeological find from the prehistory and protohistory of Poland is the Biskupin fortified settlement, dating from the Lusatian culture of the early Iron Age, the Slavic groups who would form Poland migrated to these areas in the second half of the 5th century AD.
With the Baptism of Poland the Polish rulers accepted Christianity and the authority of the Roman Church
Chromium is a chemical element with symbol Cr and atomic number 24. It is the first element in Group 6 and it is a steely-grey, lustrous and brittle metal which takes a high polish, resists tarnishing, and has a high melting point. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, Chromium metal is of high value for its high corrosion resistance and hardness. A major development was the discovery that steel could be highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating together comprise 85% of the commercial use, trivalent chromium ion is an essential nutrient in trace amounts in humans for insulin and lipid metabolism, although the issue is debated. While chromium metal and Cr ions are not considered toxic, hexavalent chromium is toxic and carcinogenic, abandoned chromium production sites often require environmental cleanup. Chromium is remarkable for its properties, it is the only elemental solid which shows antiferromagnetic ordering at room temperature.
Above 38 °C, it changes to paramagnetic, Chromium metal left standing in air is passivated by oxidation, forming a thin, surface layer. This layer is a structure only a few molecules thick. It is very dense, and prevents the diffusion of oxygen into the underlying metal and this is different from the oxide that forms on iron and carbon steel, through which elemental oxygen continues to migrate, reaching the underlying material to cause incessant rusting. Passivation can be enhanced by short contact with oxidizing acids like nitric acid, passivated chromium is stable against acids. Passivation can be removed with a reducing agent that destroys the protective oxide layer on the metal. Chromium metal treated in this way readily dissolves in weak acids, unlike such metals as iron and nickel, does not suffer from hydrogen embrittlement. However, it suffer from nitrogen embrittlement, reacting with nitrogen from air. Chromium is the 22nd most abundant element in Earths crust with a concentration of 100 ppm.
Chromium compounds are found in the environment from the erosion of chromium-containing rocks, Chromium is mined as chromite ore. About two-fifths of the ores and concentrates in the world are produced in South Africa, while Kazakhstan, Russia. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan, although rare, deposits of native chromium exist
A lapel pin is a small pin worn on clothing, often worn on the lapel of a jacket. Lapel pins can be ornamental or can indicate wearers affiliation with an organization or cause, before the popularity of wearing lapel pins, boutonnières were worn. Lapel pins are used as symbols of achievement and belonging in different organizations. Lapel pins from the organization are often collected by members and non-members alike, businesses use lapel pins to designate achievement and membership. Lapel pins are an element of employee recognition programs. Like fraternity and sorority pins, these lapel pins instill a sense of belonging to a group of performers at the organization. Businesses award lapel pins to employees more frequently to boost employee morale, the Soviet Union had great production of these. Besides pins showing political figures and as souvenirs for tourist spots, there were pins for various sports, the pins had countercultural meanings as well, for example, the pin featuring the robot spacecraft Kosmos 186 had a sexual connotation.
In recent years, pin collecting and trading has become a popular hobby. Disney pin trading is an example of this. In the 1970s, initiates of Guru Maharaj Ji extensively used buttons, sometimes quite large, senior politicians in the UKs government, wore official Games pins for the London 2012 Summer Olympics. Pin design starts off very similar to animation, everything is literally hand drawn with a blue line. It is done digitally or on paper with a light-box to plan out all of the elements. Once the design is approved, it is inked and placed on a mechanical sheet, step 1, Stamping Molding Molds the metal surface to form the design. Step 2, Outline Cutting Cutting molds are made separately, cut to the outline of the design. Additional outline cutting molds may be required depending on the complexity of the design, * If a center hole or cut-out is required, an additional cut-through mold must be used. Step 3, Attachment Solder attachment onto the back of each piece, step 4, Plating Plating now can be processed.
The quality of plating varies with the length of time the metal is soaked in the plating liquid, step 5, Polishing The metal surface is polished until it is smooth and shiny
Germany, officially the Federal Republic of Germany, is a federal parliamentary republic in central-western Europe. It includes 16 constituent states, covers an area of 357,021 square kilometres, with about 82 million inhabitants, Germany is the most populous member state of the European Union. After the United States, it is the second most popular destination in the world. Germanys capital and largest metropolis is Berlin, while its largest conurbation is the Ruhr, other major cities include Hamburg, Cologne, Stuttgart, Düsseldorf and Leipzig. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity, a region named Germania was documented before 100 AD. During the Migration Period the Germanic tribes expanded southward, beginning in the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation, in 1871, Germany became a nation state when most of the German states unified into the Prussian-dominated German Empire.
After World War I and the German Revolution of 1918–1919, the Empire was replaced by the parliamentary Weimar Republic, the establishment of the national socialist dictatorship in 1933 led to World War II and the Holocaust. After a period of Allied occupation, two German states were founded, the Federal Republic of Germany and the German Democratic Republic, in 1990, the country was reunified. In the 21st century, Germany is a power and has the worlds fourth-largest economy by nominal GDP. As a global leader in industrial and technological sectors, it is both the worlds third-largest exporter and importer of goods. Germany is a country with a very high standard of living sustained by a skilled. It upholds a social security and universal health system, environmental protection. Germany was a member of the European Economic Community in 1957. It is part of the Schengen Area, and became a co-founder of the Eurozone in 1999, Germany is a member of the United Nations, NATO, the G8, the G20, and the OECD.
The national military expenditure is the 9th highest in the world, the English word Germany derives from the Latin Germania, which came into use after Julius Caesar adopted it for the peoples east of the Rhine. This in turn descends from Proto-Germanic *þiudiskaz popular, derived from *þeudō, descended from Proto-Indo-European *tewtéh₂- people, the discovery of the Mauer 1 mandible shows that ancient humans were present in Germany at least 600,000 years ago. The oldest complete hunting weapons found anywhere in the world were discovered in a mine in Schöningen where three 380, 000-year-old wooden javelins were unearthed
Jewellery or jewelry consists of small decorative items worn for personal adornment, such as brooches, necklaces and bracelets. Jewellery may be attached to the body or the clothes, for many centuries metal, often combined with gemstones, has been the normal material for jewellery, but other materials such as shells and other plant materials may be used. It is one of the oldest type of archaeological artefact – with 100, the most widespread influence on jewellery in terms of design and style have come from Asia. Jewellery may be made from a range of materials. Gemstones and similar such as amber and coral, precious metals and shells have been widely used. In most cultures jewellery can be understood as a symbol, for its material properties, its patterns. Jewellery has been made to nearly every body part, from hairpins to toe rings. The word jewellery itself is derived from the jewel, which was anglicised from the Old French jouel. In British English, Indian English, New Zealand English, Hiberno-English, Australian English, both are used in Canadian English, though jewelry prevails by a two to one margin.
Numerous cultures store wedding dowries in the form of jewellery or make jewellery as a means to store or display coins, jewellery has been used as a currency or trade good, an example being the use of slave beads. Many items of jewellery, such as brooches and buckles, originated as functional items. Jewellery can symbolise group membership or status, wearing of amulets and devotional medals to provide protection or ward off evil is common in some cultures. These may take the form of symbols, plants, body parts, in creating jewellery, coins, or other precious items are often used, and they are typically set into precious metals. Alloys of nearly every metal known have been encountered in jewellery, for example, was common in Roman times. Modern fine jewellery usually includes gold, white gold, palladium, most contemporary gold jewellery is made of an alloy of gold, the purity of which is stated in karats, indicated by a number followed by the letter K. American gold jewellery must be of at least 10K purity, many whimsical fashions were introduced in the extravagant eighteenth century.
Cameos that were used in connection with jewellery were the attractive trinkets along with many of the objects such as brooches, ear-rings. Some of the necklets were made of pieces joined with the gold chains were in and bracelets were made sometimes to match the necklet
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through the material without being scattered. On a macroscopic scale, the photons can be said to follow Snells Law, in other words, a translucent medium allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation. The opposite property of translucency is opacity, transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. When light encounters a material, it can interact with it in different ways. These interactions depend on the wavelength of the light and the nature of the material, photons interact with an object by some combination of reflection and transmission. Some materials, such as glass and clean water, transmit much of the light that falls on them and reflect little of it. Many liquids and aqueous solutions are highly transparent, absence of structural defects and molecular structure of most liquids are mostly responsible for excellent optical transmission.
Materials which do not transmit light are called opaque, many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of light frequencies. They absorb certain portions of the spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation and this is what gives rise to color. The attenuation of light of all frequencies and wavelengths is due to the mechanisms of absorption. Transparency can provide almost perfect camouflage for animals able to achieve it and this is easier in dimly-lit or turbid seawater than in good illumination. Many marine animals such as jellyfish are highly transparent, at the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, and on selection rules. Nitrogen and oxygen are not greenhouse gases because there is no absorption because there is no molecular dipole moment.
With regard to the scattering of light, the most critical factor is the scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include, Crystalline structure, whether or not the atoms or molecules exhibit the long-range order evidenced in crystalline solids, glassy structure, scattering centers include fluctuations in density or composition. Microstructure, scattering centers include internal surfaces such as boundaries, crystallographic defects
Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog.
At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus.
From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
A necklace is an article of jewellery which is worn around the neck. Necklaces are frequently formed from a jewellery chain. Others are woven or manufactured from cloth using string or twine, common features of necklaces include colorful stones, art glass, shells, beads or corals - a hugely wide variety of other adornments have been used. If a necklace includes a primary hanging feature, it is called a pendant, if the pendant is itself a small container, necklaces are worn by both men and women in cultures around the world for purposes of adornment and social status. However, in Western society, the necklace in English often carries a female connotation. Men in Western countries often call their neck jewelry chains instead, necklaces have been an integral part of jewelry since the time of ancient civilizations and pre-date the invention of writing. Necklaces are believed to be as old as 40,000 years, during the neolithic period shell necklaces were made with the shells of 3 genera Spondylus and Charonia.
Cloth working and metalworking greatly expanded the range of available to humans. Twine and string enabled the development of smaller, more durable and glassblowing allowed faceted and highly polished gemstones and/or beautiful art glass to be added to pieces. Miniaturisation and laser etching enable the crafting of finely detailed artwork, or insignias or other calligraphy, womens necklaces are often classified by length. Choker 35 centimetres to 41 centimetres long and sits high on the neck, princess necklace A princess necklace is 45 centimetres to 50 centimetres long, longer than a choker, but shorter than a matinee. Matinee necklace A matinee length necklace is 56 centimetres to 58 centimetres long — typically a single strand that rests at the top of the cleavage, opera necklace An opera necklace is 75 centimetres to 90 centimetres long and sits at the breastbone. Rope necklace A rope necklace is any longer than opera length. Cross necklace A necklace featuring a Christian cross, diamond necklace A diamond necklace is a necklace that incorporates diamonds — they are often given as gifts in Western countries as signs of love and fealty between wealthy lovers or families.
Pearl necklace Pearl necklaces are popular among women, a bib necklace is made of multiple strands of stepped pearls. Tooth pendant necklace Some mens necklaces attach a tooth as the pendant portion. A particularly popular variant is a leather string necklace with a shark tooth attached, prayer bead necklace A long, beaded necklace typically in the form of a wide lasso, usually with a religious symbol at the end of the lasso. The beads can be made of wood, gems or even plastic
A brooch /ˈbroʊtʃ/ is a decorative jewelry item designed to be attached to garments, often to hold them closed. It is usually made of metal, often silver or gold, brooches are frequently decorated with enamel or with gemstones and may be solely for ornament or sometimes serve a practical function as a fastening, perhaps for a cloak. The earliest known brooches are from the Bronze Age, as fashions in brooches changed rather quickly, they are important chronological indicators. Many sorts of European brooches found in archaeology are usually referred to by the Latin term fibula, the fibula is an ornamental clasp used by Romans, Germanic peoples and by Celts and migratory tribes in Europe from the Early Bronze Age. They may have replaced fibulae made of more perishable Neolithic materials, fibulae are useful type-objects, carefully catalogued local typologies and distribution of fibulae can help date finds where neither numismatic nor ceramic materials provide a secure date. Fibulae were shaped somewhat like a safety pin and were used to hold clothing together.
They came in varieties and held prominent significance for the identity of the wearer, indicating ethnicity. Elaborately designed fibulae were an important part of Late Antique dress, the same types of fibulae can often be found on either side of the Roman limites, both among Roman and barbarian populations. The cultural interplay of elite objects designed to show status can be quite complex and it is likely that this type originated among Celtic groups and came to be adopted as an exotic fashion by Roman aristocrats, becoming naturalized as an important Roman emblem, and exported. From the eighteenth century through the Victorian era it was fashionable to incorporate hair, the practice began as an expression of mourning, expanded to keepsakes of loved ones who were living. Human hair was encased within the brooch or braided and woven into a band to which clasps were affixed and it was not uncommon for miniature brooch portraits to incorporate ground human hair as pigment. Two sided swivel brooches would display a portrait on one side and a lock of hair on the other, hellenic Ministry of Culture, Katie Demakopoulou, Bronze Age Jewellry in Greece Brooch.
Metropolitan jewelry, a catalog from The Metropolitan Museum of Art Libraries
The Vogtland is a region reaching across the German free states of Bavaria and Thuringia and into the Czech Republic. It overlaps with and is contained within Euregio Egrensis. The name alludes to the leadership by the Vögte of Weida, Gera. Nowadays Vogtland serves as a colloquial abbreviation for Vogtlandkreis. The landscape of the Vogtland is sometimes referred to as idyllic, bearing in mind its fields, meadows, in the south and southeast, Vogtland rises to a low or mid-height mountain range called Oberes Vogtland, or Upper Vogtland. Here, monocultural coniferous forest is the predominant form of vegetation and its mountains spread from Ore Mountains in the south-east to Fichtelgebirge in the south-west, some peaks belonging to Elstergebirge. Neighbouring regions are Frankenwald, Ore Mountains, Thüringer Schiefergebirge and Fichtelgebirge, the south-eastern part of the Vogtland belongs to Ore Mountain/Vogtland Nature Park, a protected area comparable to a national park. The river valley geography in Vogtlands north made it necessary to build comparatively big bridges to channel railroad, especially famous is the Göltzsch Viaduct for being the worlds largest bridge built of bricks and her little sister, the Elster Viaduct.
Both of them are in use as railroad bridges closing the gap between Dresden and Nuremberg, integral part of the Vogtland landscape are its reservoirs, the shores of which mostly are popular holiday and camping destinations. Plauen, the largest town, is known as the capital of the Vogtland or, with a proud note and it is thought to have been inhabited since late 7th or early 8th century by Slavic Settlers who tribally belonged to the Sorbs. Large portions of the Vogtland, were covered with pristine forests and were not settled before the High Middle Ages. Those settlers arrived mainly in eleventh and twelfth centuries, ethnically being Slavic or German, coming from areas of traditionally older settlement like Franconia, for instance, in a number of villages of the upper Vogtland even nowadays a dialect is spoken similar to that in Oberpfalz. The place name Vogtland originates in the rule of the Vogts in this region from the eleventh to the sixteenth century A. D. specifically in reference to the Vogts of Weida and Plauen.
In the 12th century, Kaiser Barbarossa appointed the first Vogts as administrators of his imperial forest areas in the East to facilitate his rule and their headquarters was the Osterburg at Weida, thus giving it the reputation as the cradle of the Vogtland. In 1349, his equinomic son Henry handed Voigtsberg over to Bohemian tenure, the exchange was heavily disputed by branch line cousins of Henrys. The Lords of Plauen, as they called themselves, retrieved Auerbach, since 1426 the Lords of Plauen were Burggraves of Meißen and found themselves in constant power struggles with the Saxonian Kurfürsts. Henry II von Plauen had fallen into disgrace with him for his opposition against nobility. Thus, Ernest received tenure over the Vogtland which, at the occasion of the Leipziger Teilung in 1485, was transferred to the House of Ernest while keeping the Bergregal under joint control
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, a range of terms are used to describe lustre, such as earthy, metallic and silky. Similarly, the term refers to a glassy lustre. A list of terms is given below. Lustre varies over a continuum, and so there are no rigid boundaries between the different types of lustre. The terms are frequently combined to describe 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, which is most notably seen in diamond, such minerals are transparent or translucent, and have a high refractive index. Minerals with an adamantine lustre are uncommon, with examples being cerussite. Minerals with a degree of lustre are referred to as subadamantine, with some examples being garnet. Dull minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, a distinction is sometimes drawn between dull minerals and earthy minerals, with the latter being coarser, and having even less lustre.
Greasy minerals resemble fat or grease, a greasy lustre often occurs in minerals containing a great abundance of microscopic inclusions, with examples including opal and cordierite. Many minerals with a greasy lustre feel greasy to the touch, metallic minerals have the lustre of polished metal, and 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 muscovite and stilbite. Resinous minerals have the appearance of resin, chewing gum or plastic, a principal example is amber, which is a form of fossilized resin. Silky minerals have an arrangement of extremely fine fibres, giving them a lustre reminiscent of silk. Examples include asbestos and the satin spar variety of gypsum, a fibrous lustre is similar, but has a coarser texture