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As mentioned before, the term “structure” means the arrangement of a material’s atoms; the structure at a microscopic scale is known as “microstructure.”
crystalline (the material’s atoms arearranged in a periodic fashion).
Some crystalline materials may be in the form of one crystal and are known as single crystals. Others consist of many crystals or grains and are known as polycrystalline.The characteristics of crystals or grains (size, shape, etc.) and that of the regions between them, known as the grain boundaries, also affect the properties of materials.

Element Allotropes Carbon• Diamond - an extremely hard, transparent crystal, with the carbon atoms arranged in a tetrahedral lattice. A poor electrical conductor. An excellent thermal conductor.
• Lonsdaleite - alsocalled hexagonal diamond.
• Graphite - a soft, black, flaky solid, a moderate electrical conductor. The C atoms are bonded in flat hexagonal lattices (graphene), which are then layered insheets.
• Linear acetylenic carbon (Carbyne)
• Amorphous carbon
• Fullerenes, including Buckminsterfullerene, aka "buckyballs", such as C60.
• Carbon nanotubes - allotropes of carbonwith a cylindrical nanostructure.
Phosphorus:
• White phosphorus - crystalline solid P4
• Red phosphorus - polymeric solid
• Scarlet phosphorus
• Violet phosphorus
• Blackphosphorus - semiconductor, analogous to graphite
Oxygen:
• dioxygen, O2 - colorless (faint blue)
• Ozone, O3 - blue
• Tetraoxygen, O4 - metastable
• Octaoxygen, O8 - red
Sulfur:• Sulfur has a large number of allotropes, second only to carbon
Selenium:
• "Red selenium," cyclo-Se8
• Gray selenium, polymeric Se
• Black selenium


Element Allotropes Boron:• Amorphous boron - brown powder - B12 regular icosahedra
• α-rhombohedral boron
• β-rhombohedral boron
• γ-orthorhombic boron
• α-tetragonal boron
• β-tetragonal boron...
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