There are two minerals that have 2 directions of cleavage at 90 nearly degrees. They are both members of the much larger group of minerals called the feldspars. Since both are feldspars they can be difficult to distinguish from one another. First let's look at the specimen carefully (use a magnifying glass or hand lens if you have one). Do you see tiny striations (parallel lines on some cleavage surfaces? If so CLICK HERE. The striations are the result of a process called twinning in which multiple crystals share a common growth plane. If you can not see any striations then you will be forced to rely on color. If the sample is white light gray or black CLICK HERE. If it is pink or blue-green CLICK HERE. Unfortunately, some varieties of orthoclase can also be white and easily mistaken for plagioclase. If neither description fits your mineral, try going back to Step 4 or Step 3