2018-01-19 : For most recent cards, looking at the expansion symbol will tell you what you need to know. Any card with a black expansion symbol is treated as a common, including basic lands. Any card with a silver expansion symbol is treated as an uncommon. Any card with a gold expansion symbol is treated as a rare. Any card with a mythic orange expansion symbol is treated as a mythic rare. Any card with a different colored expansion symbol (such as the purple expansion symbols from the Time Spiral timeshifted sheet) is treated as a special rarity. Cards from before Exodus don’t have expansion symbols. The rarities of those cards can be found on their Gatherer entries.