Garnet Types & Demantoid
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Garnet Types & Demantoid

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Questions and Answers

What is the name of the pure yellow andradite?

  • Hessonite
  • Spessartine
  • Topazolite (correct)
  • Malaya

    • What is the color range of Pyrope garnet?

  • Pinkish orange to peach color
  • Dark, purplish raspberry red to light reddish purple
  • Pale yellowish orange to dark brownish red
  • Orange-red to strongly reddish purple (correct)

    • Which type of garnet has a brownish hue and a range of orange to cinnamon colors?

  • Spessartine
  • Rhodolite
  • Malaya
  • Hessonite (correct)

    • What is the characteristic of the best Rhodolite gems?

    <p>Strong saturation and medium to medium-dark tone</p> Signup and view all the answers

    What is the name of the garnet that is a mix of pyrope, spessartine, and small amount of almandine?

    <p>Malaya</p> Signup and view all the answers

    What is the characteristic of Pyrope-Almandine Mix garnet?

    <p>Dark-toned brownish orange to brownish red to purplish red hue, with low saturation</p> Signup and view all the answers

    What is the color of Spessartine garnet?

    <p>Pale yellowish orange to bright orange</p> Signup and view all the answers

    What is the common habit of Demantoid crystals?

    <p>Rarely well-formed, more irregular nodules</p> Signup and view all the answers

    What is the characteristic of Demantoid inclusions?

    <p>Curving, radiating bundles of fibers</p> Signup and view all the answers

    What is the origin of Demantoid associated with royalty?

    <p>Russia</p> Signup and view all the answers

    What is the trade name for Demantoid with a greenish-yellow color?

    <p>Gold Green</p> Signup and view all the answers

    Where are high-quality Demantoid rough stones typically sent for cutting?

    <p>Germany's Idar-Oberstein</p> Signup and view all the answers

    What is the characteristic of Demantoid crystals that can increase their value?

    <p>Curving, radiating bundles of fibers</p> Signup and view all the answers

    What is the common size range for Demantoid used in pave settings?

    <p>Under 1ct</p> Signup and view all the answers

    What is the origin of Demantoid known for high-quality stones?

    <p>Ural Mountains in Russia</p> Signup and view all the answers

    Why is Demantoid rarely found in large sizes?

    <p>Due to its rarity</p> Signup and view all the answers

    What is the hardness of Demantoid on the Mohs scale?

    <p>6.5</p> Signup and view all the answers

    What is the best color of Demantoid garnet?

    <p>Moderately strong to strongly saturated green</p> Signup and view all the answers

    What is unique about the dispersion value of Demantoid?

    <p>It is higher than diamond</p> Signup and view all the answers

    What is Demantoid a variety of?

    <p>Andradite</p> Signup and view all the answers

    What is the color range of Demantoid?

    <p>Yellowish or brownish green hue</p> Signup and view all the answers

    What is the rarity of intense green Demantoid?

    <p>Very rare</p> Signup and view all the answers

    What is the tone of the best Demantoid color?

    <p>Medium to medium-dark</p> Signup and view all the answers

    What is the saturation level of the best Demantoid color?

    <p>Strongly saturated</p> Signup and view all the answers

    What is the characteristic hue of highly saturated Spessartine garnet?

    <p>Pale yellowish orange</p> Signup and view all the answers

    Which of the following colors is NOT a characteristic of Spessartine garnet?

    <p>Intense green</p> Signup and view all the answers

    What is the tone of highly saturated Spessartine garnet?

    <p>Medium to medium-dark</p> Signup and view all the answers

    Which of the following is NOT a characteristic of Spessartine garnet?

    <p>Weak dispersion</p> Signup and view all the answers

    What is the characteristic color range of Spessartine garnet?

    <p>Pale yellowish orange to bright orange</p> Signup and view all the answers

    What is the primary consumer market for Tsavorite?

    <p>Asia</p> Signup and view all the answers

    How does the price of a high-quality red spinel compare to a similar ruby?

    <p>It is a fraction of the price</p> Signup and view all the answers

    What is the Mohs scale hardness of Demantoid garnet?

    <p>6.5</p> Signup and view all the answers

    What is the characteristic of Mogok spinel that is highly prized by collectors?

    <p>Its 'Star of David' twinning pattern</p> Signup and view all the answers

    How many species of garnet are commercially imported as gems?

    <p>5</p> Signup and view all the answers

    What is the characteristic of the most prized Tsavorite garnets?

    <p>Their pure green color</p> Signup and view all the answers

    Which of the following elements is responsible for the color of Spessartine?

    <p>Iron and Manganese</p> Signup and view all the answers

    In which type of rocks can Spessartine be found?

    <p>Metamorphic rocks and pegmatites</p> Signup and view all the answers

    What is the characteristic of Spessartine that makes it suitable for large cuts?

    <p>It does not lose brilliance or color when cut large</p> Signup and view all the answers

    Which of the following countries is known for producing large Spessartine stones?

    <p>Nigeria</p> Signup and view all the answers

    What is the trade name for Spessartine with a dark-toned orange-red to brownish red color?

    <p>African</p> Signup and view all the answers

    Where are Spessartine rough stones typically sent for cutting?

    <p>China and Thailand</p> Signup and view all the answers

    What is the characteristic of Spessartine inclusions?

    <p>No characteristic inclusions</p> Signup and view all the answers

    Which of the following countries is not a known source of Spessartine?

    <p>Russia</p> Signup and view all the answers

    What is the crystal structure of Spessartine?

    <p>Cubic</p> Signup and view all the answers

    What is the refractive index of Spessartine?

    <p>Singly refractive</p> Signup and view all the answers

    Study Notes

    Garnet Types and Characteristics

    • Topazolite: a pure yellow andradite
    • Spessartine: pale yellowish orange to dark brownish red, with a highly saturated, reddish orange hue and medium to medium-dark tone
    • Malaya: a pinkish orange mix of pyrope, spessartine, and almandine, often referred to as "peach" or "cinnamon"
    • Hessonite: an orange to cinnamon-colored variety of grossular garnet with a brownish hue
    • Rhodolite: a range of dark, purplish raspberry red to light reddish purple, with a medium to medium-dark tone and strong saturation

    Garnet Chemical Composition

    • Garnet: basic composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible
    • Tsavorite: a trace element of vanadium
    • Demantoid: a trace element of chromium and iron
    • Spessartine: a trace element of manganese and iron
    • Hessonite: a trace element of manganese and iron
    • Pyrope: top stones have a trace element of chromium and iron, with less vibrant hues
    • Spinel: intense reds and pinks are caused by traces of chromium, while orange and purple stones owe their color to a mixture of iron and chromium

    Forming Sources

    • Garnets: formed in metamorphic rocks and pegmatite veins
    • Demantoid: formed in volcanic and metamorphic rocks
    • Spessartine: formed in pegmatites and metamorphic rocks
    • Rhodolite: formed in alluvial deposits and metamorphic rocks
    • Almandine: formed in metamorphic rocks like schist
    • Spinel: formed in marble and alluvial deposits

    Crystal Structure

    • Garnets: all have a cubic crystal system, with the most common habit being dodecahedron
    • Tsavorite: rarely forms well-formed crystals, often in irregular nodules called "potatoes" or "pods"
    • Spinel: has a cubic crystal system, with a crystal habit of an octahedron, and can form flattened twin crystals

    Clarity and Inclusions

    • Garnet and Spinel: are singly refractive
    • Tsavorite: has an extinction in darker stones
    • Demantoid: has curving, radiating bundles of fibers known as "horsetails", which can increase the value of a stone
    • Hessonite: most hessonite is highly included, with inclusions causing an instantly recognizable "heat wave" or "scotch-in-water" effect

    Garnet Species

    • There are 20 garnet species, with only 5 commercially imported as gems.
    • Many garnets are mixtures of two or more garnet species.

    Demantoid

    • A variety of andradite garnet.
    • Chemical composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible.
    • Trace elements of chromium and iron.
    • Found in volcanic and metamorphic rocks.
    • Rarely forms well-shaped crystals, often occurs in irregular nodules called "potatoes" or "pods".
    • Crystal system is cubic.
    • Singly refractive.
    • Characterized by curving, radiating bundles of fibers known as “horsetails”.
    • Often used in pave settings, rarely found over 3ct.

    Tsavorite

    • A variety of grossular garnet.
    • Chemical composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible.
    • Trace element of vanadium.
    • Found in metamorphic rocks and pegmatite veins.
    • Rarely forms well-shaped crystals.
    • Crystal system is cubic.
    • Singly refractive.
    • Calibrated squares, rounds, and ovals under one carat are popular.
    • Larger stones (7×5 mm and larger) are more rare.

    Spessartine

    • Chemical composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible.
    • Trace elements of manganese and iron.
    • Found in pegmatites and metamorphic rocks.
    • Can be cut large without losing brilliance or color.
    • Often cut into calibrated shapes, including rounds, ovals, octagons, squares, hearts, pear shapes, and trillions.

    Rhodolite

    • A mixture of pyrope and almandine garnet.
    • Found in alluvial deposits and metamorphic rock.
    • Good for being calibrated, prices rise steeply at 10ct and above.
    • Often cut into free form cuts by lapidary designers.

    Pyrope

    • Chemical composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible.
    • Trace elements of chromium, iron.
    • Found in metamorphic rocks.
    • Small red brilliant-cut or rose-cut pyropes are common.

    Almandine

    • Chemical composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible.
    • Trace elements of iron.
    • Found in metamorphic rocks like schist.
    • Often cut as a cabochon with a curved undercut bottom, known as a "hollowback".
    • Reflective foil backings can improve their dark appearance.

    Pyrope-Almandine Mix (not Rhodolite)

    • Chemical composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible.
    • Calibrated shapes, including rounds, ovals, octagons, squares, hearts, pear shapes, and trillions.
    • Larger carats have darker tone and are often cut to shallow proportions.

    Hessonite

    • A variety of grossular garnet.
    • Chemical composition is silicon, oxygen, and aluminum, with isomorphous replacement being possible.
    • Trace elements of manganese and iron.
    • Found in metamorphic rocks.
    • Often too included to be used in jewelry, crystal inclusions—usually apatite, diopside, and zircon.
    • Characterized by an instantly recognizable “heat wave” or “scotch-in-water” effect.

    Spinel

    • Chemical composition is oxygen, magnesium, aluminum, and silicon.
    • Intense reds and pinks are caused by traces of chromium.
    • Orange and purple stones owe their color to a mixture of iron and chromium.
    • Found in marble and alluvial deposits.
    • Crystal system is cubic.
    • Singly refractive.
    • Formatted into octahedral crystals, can form flattened twin crystals.
    • Flux-grown synthetic spinel is also manufactured into triplets.
    • Bright, very intense pink spinels command high prices amongst collectors.

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    Stone Info Garnet & Spinel PDF

    Description

    Test your knowledge of the different types of garnet gemstones, including their unique colors and characteristics. From Spessartine to Hessonite, learn about the distinct hues and tones of each variety. Can you identify the differences between these precious stones?

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