There are some key field in the tweet JSON data to help us understand the purpose of this tweet.
retweeted_status,tweetobjectquoted_status,tweetobjectin_reply_to_status_id,int64, a pointer to tweet object
(1) If none of these fields is populated (not null), then this is a normal tweet or original tweet. It happends when you write some text and post it on twitter.
(2) If retweeted_status is populated, then this is a retweet. It happends when you click retweet button to repost other's tweets without comment.
(3) If in_reply_to_status_id is populated, then this is a reply tweet. It happends when you click reply button and reply to other's tweets.
(4) If quoted_status is populated AND other two fields are not populated, then this is a quoted tweet. It happens when you retweet other's tweets with comment, OR you use the URL of other's status in your post.