Sentence:  It was amazing how they had herded together for protection : an enormous matriarch in a quilted silk wrapper , rising from the breakfast table ; a gross boy in his teens , shuffling in from the kitchen with a sandwich in his hands ; a girl in her twenties , fat and sullen , descending the <WSD>marble</WSD> staircase ; then all four gathering on the sofa to face the inquisitor . 
Meaning of the word marked with <WSD> tags:  a hard crystalline metamorphic rock that takes a high polish; used for sculpture and as building material