Formula: Pb20(SiO4)7(SO4)4Cl4
Origin of name: For Matthew Heddle, Scottish mineralogist
Crystal system: Hexagonal
Crystal class: 6/m
Twinning:
Unit cell:
Colour: Creamy white
Diaphaneity:
Luster: Adamantine
Habit: Radiating hexagonal prisms to 10-20 µm x 100 µm forming aggregates and linings
Hardness:
Specific gravity: 6.96
Cleavage: 1; basal
Tenacity:
Streak: White
Synonyms/varieties:
Comments: Fluoresces dull yellow under SW
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