Calcite is used to determine the difficulty of Mohs mining. Your nail is about 2½ hard, so you can not scratch calcite. Usually, these thick and white beans, healing beans appear, but other colors may also be colored. If the hardness and appearance of calcite is not sufficient, acid test, in which the hydrochloric acid (or white vinegar) is diluted, creates carbon dioxide bubbles on the surface of the mineral, a definitive test.
This is not a real crystal, but a fragment of the gap. Calcite is said to have a rhombogram cleft, because each of its faces is a fox or a rectangle wrapped in which none of the corners is square. When fine crystals are formed, calcite forms shapes that are full of shape or lacquer, the usual name of which is “ribs”.
If you look at a piece of calcite, the objects behind the sample will be offset and doubled. This offset is due to the deviation of the light through the crystal, so that a stick appears to bend when you do it continuously to the water. The doubling is due to the fact that light differs in different directions in crystals differently. Classic is a classic reflexive example, but it’s not rare in other minerals.