Honey changing into unusable, hardened clump I buy raw, unfiltered honey from the grocery store in jars sold/packed directly by the farmer.
When I had used the last jar to about half, I noticed the honey beginning to dry(crystalize?) to the point where I couldn't use the honey around these spots. 
Not too long after this, the entire jar had crystallized into a block of unusable hard stuff. 

I didn't do anything differently with this jar than the last jar, but only now am I having the issue. My question(s): 

Why is the honey crystallizing, and why so rapidly? 

1) Is the honey unusable at this point?

2) Should I store the honey differently after purchasing it(move from jar to other container)?

3) I've never seen this happen to the filtered, strained(fake) honey from the store, so what causes this to happen in the raw and unfiltered form?
Honey is entirely useable after crystallization. This is a natural and spontaneous process and doesn't affect the honey negatively in terms of flavor or quality. It's dependent upon the sugar content of the particular honey, and in particular the crystallization speed is determined by:


the nectar source collected by bees (the sugar composition of honey),
the methods in which honey is handled (processed) and
the temperature in preservation.


To re-liquefy, gently heat it in a water bath in its container, up to 40&deg;C (104 &deg;F) - the temperature of a beehive in the summer. Beyond this will damage the honey.

Don't store honey in a cold area - the optimum temperature is 20-27 &deg;C (70-80 &deg;F). Ideal crystal formation occurs at 11-18 &deg;C (52-64 &deg;F), and storing in the refrigerator accelerates the process. 

More information in the PDF at the bottom of this post.

Reference:


www.montcobeekeepers.org/Documents/Honey_Crystallization.pdf