Ronald Reagan

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The Smithsonian is a renowned research center, dedicated to public education, national service, and scholarship in the arts, sciences, and history.

Jeffrey E. A catalog record for this book is available from the Library of Congress. ISBN DK books are available at special discounts when purchased in bulk for sales promotions, premiums, fund-raising, or educational use. Physical properties Crystal systems and habits What is a gem?

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Visual properties Where do gems come from? Grading and evaluation Gem cuts The value of a gem What is a jewel? From sunken pirate ships to wicked diamonds to cities of gold, its sinister sparkle has a singular ability to bring out the very best and the very worst in each of us. History, mythology, or pure fantasy, the best stories all have that one thing in common: they all have something glittering at their heart.

But this book is not a story.

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A story has a beginning, a middle, and an end. This book is a map, a codex, a tool to help you understand all of those other stories. The hard science; the facts. The story of stones is about beauty and desire, status and symbolism. Gems were one of the first currencies, and to this day are the marker by which we judge monetary value.

But what makes gemstones so valuable, so powerful?

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Gems have been considered both poisons and medicines and some actually arebarometers of everything from truth to danger. Occasionally their power even strays from the symbolic to the literal, resulting in cults, relics, and legends of cursed gems.

Wars have been fought, industries have been created, and empires have risen and fallen, all in pursuit of that which is beautiful, valuable, and rare. Surely to desire, to covet, is human.

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As is the tendency to worship, to adorn, one might even say to treasure. But what catches the eye? What draws us to anything?

A bright color? A flash of light? What is it about gems that so uniquely compels and possesses us? How have these glittering bits of the world had such power over our hearts and our minds throughout history? Free will be damned. The vmPFC also plays a vital role in our assessment of morality. But that singular human weakness for beauty and a collective obsession with gemstones goes dating oceanside ca than emotional neurochemistry.

Our need to see and possess glowing, shining jewels is as intrinsic to what we are, as to who we are.

Another objective fact: we see certain colors more vividly and more clearly than we see este mj încă dating charlie pe shahs of sunset else. And even more so to shine, and above all to sparkle. It was our first and still our most basic need—the need for water—that taught us to seek and to value that which glitters and shines. In a very real sense, sparkles equal life. The story of stones must be chipped away at, rock by rock.

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It is the very story of humanity. From the crowns of the earliest chieftains, to modern diamond semiconductors, every age is the Stone Age. The story of stones is the story of us. Many of these began as mineral crystals that formed as a result of geological changes over millennia. The crystals are extracted, then cut, faceted, and polished to be used in jewelry and other decorative items.

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Organic gems are made of biologically derived matter, such as Three rock types Minerals Beveled, tabular crystal, typical of the mineral wulfenite Components of the Earth There are three major classes of rock: igneous, sedimentary, and metamorphic. Igneous rocks are either formed from magma molten rock that has solidified underground, creating intrusive rocks such as granite, or has flowed onto the land or seabed, forming extrusive rocks such as basalt.

Metamorphic rocks are formed when the mineralogical composition of existing rocks is altered by heat or pressure. Quartzite, for example, is metamorphosed sandstone.

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Igneous rock This example of intrusive igneous rock, granite, is formed inside the Earth when magma cools. Tiny crystals can be seen on its surface. Sedimentary rock Sandstone usually contains quartz but other minerals can also be present. This example shows patches of iron oxide and flakes of mica. Metamorphic rock The component minerals of gneiss— mainly quartz and feldspar—tend to separate out into distinct bands of different colors.

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The financial worth and perceived value of these precious materials can vary from society to society—in some cultures, jade is more valuable than gold, for example. Rubies are among the most highly valued gemstones in the West—the Most gems are cut crystals of minerals. A mineral is defined as a naturally occurring solid with a specific chemical composition and a distinctive crystal structure see pp.

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Each mineral has a unique name based on these two criteria. If either of these changes, it becomes a different mineral with a different name. All rocks begin as igneous, but over time they are altered by remelting, erosion, or metamorphosis— weathering and erosion lead to the formation of sedimentary rock, which can turn into metamorphic rock through temperature or pressure conditions.

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Other types of gem, released from their original rock by weathering, can be mined from placer deposits found in stream gravels. Examples of these varieties include topaz, sapphire, chrysoberyl, garnet, zircon, and spinel. The rock cycle This diagram shows how different types of rock are formed. Uplift to surface Burial, sedimentation Gem deposits Gems such as rubies red corundum and sapphires corundum in other colors can be recovered from the rocks in which they form, or from placer deposits.

Weathering Rock veins containing corundum sapphire, ruby Transportation Placer deposits with concentration of heavy sapphire and ruby Metamorphic rock Pressure and heat Stream Rock veins containing corundum sapphire, ruby Sedimentary rock Polished copper and silver in a rock matrix Crystals Native elements A crystal is a solid, the component atoms of which are arranged in a particular, repeating, three-dimensional pattern.

When these internal patterns produce a series of external, flat faces arranged geometrically, a crystal, such as the rhodochrosite above, is created. These are chemical elements that occur in nature uncombined with other elements see also p. With the exception of platinum and gold, most metals are extracted from minerals that contain them. Stalactitic amber Organic gems Created through organic processes, organic gems are not commonly crystalline.

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Jet is a form of coal, derived from plant matter; coral and shell are the secreted skeletons of marine animals, while pearls are formed by shelled mollusks; and amber and copal are tree resins, fossilized and semifossilized. Organic gems are generally softer than minerals and easier to work. Each one has its own unique chemical composition and internal atomic structure—indeed, a mineral is defined by its chemical elements and by the atomic structure of its crystallization.

Minerals are usually formed by inorganic processes, although there are organically produced substances such as the hydroxylapatite in teeth and bones that are also considered minerals.

Certain substances, including opal and glass, resemble minerals in appearance, Mineral classification Minerals are grouped according to their chemical composition. A mineral compound has positively and negatively charged atoms or groups of atoms: the element or elements that carry the negative electrical charge determine which chemical group a mineral is assigned to.

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The largest mineral group, the silicates, is further divided into six subgroups based on their different chemical structures. Gold nugget Fluorite crystals chemistry, and occurrence, but do not have a regularly ordered internal arrangement and so do not exhibit crystallinity: este mj încă dating charlie pe shahs of sunset are known as mineraloids. However, most minerals are chemical compounds, composed of two or more chemical elements.

There are around types of mineral that are considered common, out of more than 5, known minerals. Delicate bluecolored crystals.