Simple categories matching birefringent:

• particle,
• mineral,
• crystal,
• layer,
• material,
• structure,
• fiber,
• part,
• substrate,

Members with property birefringent:

• composite_sheet,
• radial_fiber,
• bowtie_fiber,
• sapphire,
• quartz,
• calcite,
• lithium,
• mica,
• rutile,
• plant-cell_wall,
• pyroxene,
• crystalline_quartz,
• starch,
• nerve-fiber_layer,
• dust,
• spindle,
• polymer,
• epoxy,
• lens,
• mineral,
• collagen_fiber,
• rutile_crystal,
• size,
• panda_fiber,
• yttrium_vanadate,
• gypsum,
• quarter,
• birefringent_patch,
• starch_grain,
• collagen,
• fibre,
• tourmaline,
• elliptical_jacket,
• ash,
• calcite_material,
• mitotic_spindle,
• magnesium_fluoride,
• cytoskeleton,
• cholesterol,
• cellulose,
• crystal_quartz,
• talc,
• olivine,
• ground_mineral,