Category: Asymmetrical/Irregular habits
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Sceptered – Crystal growth stops and continues at the top of the crystal, but not at the bottom
Common examples include: hedenbergite, quartz
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Nodular/Tuberose – Deposit of roughly spherical form with irregular protuberances
Common examples include: agate (and other chalcedony)
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Massive/Compact – Shapeless, no distinctive external crystal shape
Common examples include: limonite, turquoise, cinnabar, quartz, realgar, lazurite
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Hemimorphic – Doubly terminated crystal with two differently shaped ends
Common examples include: hemimorphite, elbaite
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Amygdaloidal – Like embedded almonds
Common examples include: heulandite, subhedral zircon Amygdules or amygdales (/əˈmɪɡdjuːlz, -deɪlz/) form when the vesicles (pores from gas bubbles in lava) of a volcanic rock or other extrusive igneous rock are infilled with a secondary mineral, such as calcite, quartz, chlorite, or one of the zeolites. Amygdules usually form after the rock has been emplaced, and are often associated with low-temperature alteration. Amygdules may often be concentrically zoned. Rocks containing amygdules can be…