The Coeur d'Alene Mining District in Silver Valley, ID is known for its large lead deposits of the mineral galena (PbS). Galena is one of the few common minerals with a metallic luster that has a distinctive cleavage (cleavage is how a mineral breaks or parts along preexisting planes of weakness). Cleavage is described by the number of unique directions of cleavage planes and the angle between those planes. Which of the following best describes galena’s cleavage? a. three directions at ~90°
b. three directions not at ~90°
c. two directions at ~90°
d. two directions not at ~90°