In hearthstone each card has a rarity that stands for how difficult the card is to acquire. The five different rarities a card can have are free, common, rare, epic, and legendary. As you would expect, the higher the rarity of a card the more powerful it tends to be and the more expensive it is to craft out of dust.

The rarity is represented on each card by a color coded gem located in the centre, underneath the portrait. Free (or basic) cards are an exception to this as they don't come with any gems whatsoever. Free cards are the cards everyone receives right off the bat, hence the name "free". Cards with a rarity higher than free can be constructed with dust, or picked up from a card pack.

Free Cards

There are 59 free cards in the Hearthstone card collection. These free cards are all a part of the "basic set" of each class, and the starting neutral cards each player receives when they first start the game. You will receive two of each free card, both class and neutral. Some example of free cards are the Sen'jin Shieldmaster, Northshire Cleric, and Arcane Missiles.

Common Cards

Next up in the rankings are common cards, represented by a white gem. There are over 150 cards classified as common, making then the largest rarity category in the game. As the name suggests, they are also the most common rarity of card found in the card packs.

While you get the basic free class cards right off the bat, the basic common class cards can be added to your collection by levelling each class to 10, and expert common cards from card packs or crafting. Golden versions of many of these cards can also be obtained by levelling the class even further.

Rare Cards

Filling in the mid range spot are the rare cards that make up about 25% of the total cards in Hearthstone. You can tell a rare card by the blue gem underneath the portrait. The only way to get rare cards is randomly through expert card packs, and by crafting with dust. The amount of dust required to craft rare cards is usually double that of common cards.

 Epic Cards

A purple gem signifies an epic card which is second in rarity only to the legendary cards. There are only 38 epic cards currently available in the entire hearthstone card library. The only way to get your hands on epic cards is to get them from an expert pack, or craft them directly. Epic cards are significantly more expensive to craft than rare cards, at least 400 dust.

Legendary Cards

The top tier cards available in hearthstone, these cards are almost always representations of powerful individuals from the World of Warcraft universe. Their cards are elaborately decorated with a dragon crest along the top, and an orange gem under the portrait. Currently there are only 36 legendary cards in the Hearthstone collection, making them the rarest. Of course being this rare, they are also some of the most powerful cards in the game and boast big stats and very unique and powerful battlecries.

Due to the power of legendary cards, only one of each card can be used in a deck. The majority of legendary cards can only be obtained through crafting or expert packs, while a few can be picked up as reward sets.