Ursilite

Formula: (Mg,Ca)₈(UO₂)₈(Si₂O₅)₁₁(OH)₁₀·26H₂O

Origin of name: for its uranium and silicate content

Crystal system: Orthorhombic, probably metamict

Crystal class: 

Twinning: 

Unit cell: a = 14.1, b = 35.7, c = 14.3
 

Colour: Lemon yellow, light yellow

Diaphaneity: 

Luster: Vitreous, silky

Habit: Radiating aggregates, massive lenticular clusters to 1 cm, coatings

Hardness: 2-3

Specific gravity: 3.18

Cleavage: 1; (100}

Tenacity: 

Streak: Straw yellow to light yellow

Synonyms/varieties:

Comments:  Radioactive