Something like this?
Secrete Crystal (Ex): A j'hol can secrete a liquid that quickly hardens into a crystalline substance. A j'hol can produce up to x pounds of crystal each day, which may be used as raw materials in the creation of any item that could normally be crafted from wood, stone, or metal. A weapon or armor created with this crystal functions exactly the same as its wood, stone, or metal counterparts, except the crystal has hardness x and x hit points per inch of thickness. Crystalline items may be enhanced my magic as if they were a wood, stone, or metal item. Crystalline items are more susceptible to shatter spells (see the shatter spell description) and similar effects.