Formation: In hydrothermal vents and hot water environments in connection to thermal heating.
Unusual Properties: Realgar is one of the minerals that contains arsenic, a deadly poison. And simply handling the mineral can put one at risk of arsenic poisoning. When heated it gives off a strong smell of garlic. As shown above, the crystals are a beautiful red color and are short prisms. And often occur in conjunction with calcite as shown here. This is a beautiful and interesting mineral to add to your collection, but definitely one to keep under lock at key if you have children in the house. In fact, the mineral dealer who sold me this specimen had it in a locked show case. Words to the wise regarding realgar.