Card Packs, or Basic Boosters, are bought from the Chronicle's Store for 1000 Copper Coins. Each Card Pack contains 5 Cards, of which contains at least 1 Emerald or higher rarity card.
Statistical Analysis Edit
Here is a large sample of opened card packs to give you an idea of how rare it is to receive certain rarity cards:
Total Packs: 79 / Total Cards: 395