incrustation

incrustation
/ˌɪnkrʌˈsteɪʃn; ˌɪnkrʌs`teʃən/ n
1 [U] formation of a hard outer covering; encrusting 结皮; 形成硬壳.
2 [C] hard outer covering or layer, esp one that forms gradually 硬壳, 外层（尤指逐渐形成的）
    incrustations of barnacles on the hull 藤壶附在船身上形成坚硬的外层.

牛津英汉双解词典