shardkey

[Joshi, Shital]

Hi,

We are using Solr 4.3.0 SolrCloud (5 shards, 10 replicas). I have couple 
questions on shard key. 

        1. Looking at the admin GUI, how do I know which field is being used 
for shard key.
        2. What is the default shard key used?
        3. How do I override the default shard key?

Thanks.