Shell Gemstone & Information | Gemopedia by JTV | Gemopedia™
Shells were one of the first items used for ornamentation, and for good reason. Unique, one-of-a-kind shells have their own allure and appealing, natural beauty. Formed as the hard outer covering of many mollusks, shell is grown in layers by cells in the mantle, a skin-like tissue in the mollusk's body wall. As there are many varieties of mollusk, shells come in an endless array of shapes, sizes, and colors.
White, Gray, Brown, Yellow, Orange, Pink
Shell classificationCommonNameShellSpeciesNAVarietyColorsWhite, Gray, Brown, Yellow, Orange, PinkAlternateNamesGemstoneGroupsKeySeparationsAppearance, RI, birefringence blink and magnification.ClassificationCommentsMisnomers: Chinese cat's-eye, shell cat's-eye Helmut shell are usually carved as cameos, generally layered in two colors, white and brown or white and orangeConch shell: pink to orangeOperculum: white, green and brown with eye-like appearance
Shell chemistry & crystallographyChemicalNamecalcium carbonate, conchiolin and waterChemicalFormulaCaCO3 with H2O and other organic materialsSynthesisCrystalSystemNAChemistryClassificationOrganicNatureNaturalCrystallinityNon-CrystallineChemistryComments
Shell optical propertiesTransparencyTranslucent - OpaqueDispersionOpticalCommentsRefractiveIndex1.53-1.685Birefringence0.155OpticCharacterOpticSignPolariscopeReactionAggregate (AGG)FluorescenceSWUV: Variable
Shell characteristic physical propertiesHardness3.5CharacteristicCommentsStreakSpecificGravity2.7-2.89 Typical:2.86ToughnessFairInclusionsShell cameos will show concave backs due to structure of the shell. Shells might show orient and will have a parallel growth structure.Helmut shell cameos will have a straight irregular fibrous structure and concave back.Operculum is the eye-like marking on the front and spiral growth on the back of a shell.Conch shells will have a flame-like structure.LusterGreasyStabilityFractureUneven, SplinteryCleavageNone