GEMS 331 Final Exam | Questions and Answers

GEMS 331 Final Exam | Questions and Answers The refractive index (RI) of a gem relates to light as it ___. enters or exits the surface of a gemstone Brilliance is described as ___. the amount of light reflected from within the stone Diamond has a hardness of ___. 10 The bottom-most facet of a gemstone is called _____. The culet Rubies and sapphires are made of ___. Aluminum Oxide (Al2O3) Rubies are red due to ___, while sapphires are blue because of___. Chromium ions, Titanium and Iron ions Synthetic Rubies are made from _____ while Ruby simulants are _____. Aluminum oxide, Spinel Corundum has a hardness of 9 Pleochroism is the change of colors when viewed from different angles Which of the following would best indicate you have a synthetic ruby? Curved striae on surface of stone. Peridot is a gem variety of Olivine Beryl will not form without the presence of what element? Beryllium The chemical structure of Olivine is (Mg, Fe)2SiO4 Which of the following statements about fire in gemstones is false? Fire is created when facets of a cut gemstone are parallel to each other. Color in gems may come from _____. inclusion, and reflection of specific colors A one (1) carat diamond is worth more than a two (2) carat diamond if: Compared to the two carat gem, the one carat gem has proper facets, and is quite clear A four carat diamond (A) will be worth more than another of the same weight (B) if: The second diamond (B) has cracks or appears cloudy. (This is the only answer that makes diamond (A) more valuable. This is another aspect of the "4 C's" concept. The more clear a gem is, the more valuable it will be.) The term 'metamorphism' refers to: the process by which rocks are changed by heat and pressure Pegmatites are ___. igneous rocks with very large crystals (more right) hydrothermal deposits with large crystals "Cleavage" refers to the tendency of a mineral to break along planes of atomic weakness Refraction to bend light as it passes from air to the crystal Igneous rocks are ___. formed from hot, molten rock or magma Metamorphic rocks are sedimentary or igneous rocks changed by elevated temperature and pressure A well cut stone should internally reflect light at the pavilion facets (The light is reflected back up, and passes out of the top of the gemstone (the crown)) The mantle is ___. the semi-solid layer of rock below the crust (whether it's semi-solid, semi-hard, semi-soft, or plastic, it means that it does not behave as a brittle solid.) The cut of a stone refers to: The way a gem is faceted The emerald cut is so named because: the namesake stone is commonly fashioned that way The brilliant cut is primarily used... ...to enhance the sparkle of a diamond. Diamond is the hardest mineral. Graphite is the softest mineral. They both are made from ___. Carbon One carat equals ____ grams. 0.2 With two given stones of the same quality (same color, cut, and clarity) the ____ will always be more valuable. the larger one (if all the other "C's" are equal) (Synthetics are often less valuable than their natural counterparts.) Heat treatment of sapphires results in ___. None of them. NOT Increased rutile inclusions, NOT increasing the refractive index of a gem, NOT oiling the surface to make it more opaque, and NOT removing blue light wavelengths from within the gem Which of these is the least symmetrical crystal system? Monoclinic Opal differs from crystalline quartz because ___. Opal can contain a great deal of water, while quartz contains none. Pleochroism may be important when Choosing the orientation in which the gem is cut, because this will affect the color observed. (and maybe when determining the carat weight) Light is bent when it passes into a crystal because the density of the crystal is greater than the density of air, interaction of light with atoms decreases the wavelength of light (A change in density causes light to refract. Light is bent when it passes from a material of one density (like air, which has low density) to a material of a different density (like the stone). Which of the following crystal systems is the most symmetrical? Cubic Citrine is a type of SiO2 containing Fe impurity often formed by heat treatment of amethyst (and maybe an amorphous quartz variety made of balls of silica) Which of the statements about allochromatic minerals is false? Color in sapphires is due to the absorption of blue light wavelengths by Fe and Ti ions. Crystal structures are made of repeated unit cells. Which of the following is NOT analogous to the unit cell concept? A single duck in a large flock of geese. Color in gemstones is often produced by ___. All of them: Color centers, absorption of specific light wavelengths, reflection of specific light wavelengths, and impurities A gem must be cut to specific dimensions because: the index of refraction will bend light only a specific amount. Critical angle is the angle, calculated from the refractive index, that determines whether or not light is internally reflected Reflection is ____ while refraction is ___. when light bounces off the surface of the gem, when light bends inside the gemstone the most symmetrical crystal system is the ___ system. Cubic Something is crystalline if the atoms in a solid are in a periodic arrangement (Not all solids are crystalline. To be crystalline a material must be solid AND have its atoms in a periodic arrangement. Opal is an example of a non crystalline solid.) The angle at which light is completely reflected from the surface of a gem is ____. Critical angle (Normal: the normal is just a reference line - perpendicular to the surface that the light is hitting. Acute Angle: An acute angle is just an angle less than 90 degrees. There is no indication given in the notes that this has to be an acute angle. Snell's Law: This is the mathematical relationship between the refractive index and the angle of incedence. This is independent of any specific angle at which light may strike the surface. Refractive Index: The refractive index is a measure of the speed of light in air versus that of around a gem. It is not an angle in and of itself. Critical Angle: This is the correct answer. The critical angle is "specifically the angle at which total internal reflection occurs." Many of you were hung up on the word surface. I recommend you look at a gem again. Or even look at a swimming pool. Internal reflection occurs at the surface interface with the air. It is possible, and is the basis of the definition, that the light is reflected from the surface of a gem. This is true REGARDLESS of whether the light is coming above from outside, or below from inside the gem.) Which of the following is not a name for a variety of Topaz? "brazil" Ideally, true gemstones should be many things except ____. Synthetic Citrine is a type of SiO2 containing Fe impurity often formed by heat treatment of amethyst If abundance at the surface of the earth were the only measure of value, what would be the least valuable gem? Amethyst (The more rare a gem, the more valuable it would be. Of the gems listed, quartz is the most common. Since I clearly stated that abundance is the only factor here, quartz would be the least valuable. The other choices do not have any clear correlation with abundance.) Olivine is found within ___ rocks, which are ___ in origin. basalt, igneous Crystalline quartz has a hardness of ___. 7 In the near future, a lunar mining expedition discovers a new mineral, Unobtanium. This mineral displays many remarkable properties, not the least of which is it has a hardness of 11 on Moh's scale. In order to form a gemstone out of this new mineral, what should a gem cutter use to cut and polish the facets? Anything harder than quartz Spodumene and Kunzite are varieties of what mineral? Pyroxene What color will red construction paper appear in blue light? Black The 6-pointed stars seen in certain rubies and sapphires are due to numerous fine rutile needle inclusions in orientations at 60 degrees to each other (The stars are due to rutile (TiO2) crystals in the ruby or sapphire. These crystals are parallel to the hexagonal faces and thus in three orientations.) A likely candidate for an alluvial gemstone is ____. Ruby The popular blue color of topaz can be achieved by ____. irradiation followed by heat treatment to selectively remove yellow and red color centers Which of the following statements about crystals is false? Although made of a regular arrangement of atoms, most crystals do not consist of repeated unit cells. All of the following are true: The unit cell of a quartz crystal is a silica tetrahedron, The least symmetrical arrangements of atoms are found in the triclinic crystal system, Minerals from any of the six crystal systems can develop euhedral crystals, If the most symmetrical crystal in the world was spherically shaped, it would still be placed in the cubic crystal system. Neolithic tools were sometimes made of ____. Nephrite What is the gemstone variety of Andradite? Demantoid Asterism is the result of _____. Rutile needle inclusions Electrons are ____ in ionic bonds and are _____ in covalent bonds. exchanged, shared Garnets contained All of them: A divalent cation, a trivalent cation, and silica tetrahedron Long, fibrous inclusions in gemstones may produce ____. All of them: chatoyancy, asterism, and opacity Which of the following statements about gem enhancement is false? Because enhancements are done to improve the appearance of a stone, enhancements always increase the value of a gem. Chromophores are present in all varieties of quartz except ____. Rock Crystal A cleavage fragment of calcite will NOT ____. have a different chemical structure If we were to assign the Great Pyramid at Giza to a crystal system, what is the best choice? Cubic If you were looking for real gold, you should be most excited to find ____. Milky Quartz Color enhancement is intended to produce ____. All of the above: color centers, dissolved rutile, and greater clarity The brownish color in some peridot (olivine) is due to ___. A significant iron content (Peridot, or olivine, is (Mg,Fe)SiO4. The brown color comes from the presence of iron in the mineral.) You find a clear green gem with a specific gravity of about 4, and a dodecahedron-shaped crystal. This is most likely a ____. Most likely: Pyralspite Garnet, but also Ugrandite Garnet (Pyralspite garnets are more common than Ugrandite garnets) An aventurescent feldspar gem is ____. Sunstone Peridot is the gem form of ___. Olivine A four carat diamond (A) will be worth more than another of the same weight (B) if: The second diamond (B) has cracks or appears cloudy. (This is the only answer that makes diamond (A) more valuable. This is another aspect of the "4 C's" concept. The more clear a gem is, the more valuable it will be.) Diamond has a hardness of ___. 10 The more inclusions a gem has, the ______. All of the above: less valuable it will be, more fragile it may be, and the more cloudy it will appear A true gemstone is _____. Naturally occurring Cabochons are Convex with a flat bottom The largest diamond in the world, the Cullinan, weighed nearly 3,107 carats (before cutting). How many grams is this? 621 g The bottom-most facet of a gemstone is called _____. the culet Brilliance is described as ___. the amount of light reflected from within the stone The top-most facet of a gemstone is called the: Table Sedimentary rocks are where turquoise forms All oxides contain ___. Oxygen The most common mineral in the mantle is Olivine The four most common elements in the earth's crust are ____. Oxygen, Aluminum, Iron, Silicon The periodic table is a table that arranges elements in order of increasing number of protons Carbon can have several isotopes. What does this mean? There can be a varying number of neutrons in the nucleus of a carbon atom The element Technetium has an atomic number of 43. What does this number mean? The total number of protons in the element Match the following minerals with their equivalent hardnesses. 1: Talc 2:Gypsum 3: Calcite 4: Fluorite 5: Apatite 6: Feldspar 7: Quartz 8: Topaz 9: Corundum 10: Diamond Critical angle is ____. the angle, calculated from the refractive index, that determines whether or not light is internally reflected The refractive index (RI) of a gem relates to light as it ___. enters or exits the surface of a gemstone Reflection is ____ while refraction is ___.