You are correct that "à partir de" suggests that but it is conveyed into English with "from". Across languages, each word need not have an exact counterpart when the sentence is translated to communicate the same meaning. http://dictionnaire.reverso.net/francais-anglais/%C3%A0%20partir%20de
The key to understand the two primary expressions is this:
- "xxx est fait à partir de yyy" means that xxx is made FROM yyy, i.e., yyy is the raw material which is transformed through a process so that it becomes xxx.
- "xxx est en yyy" means that "xxx" is made of "yyy". The process of turning "yyy" into "xxx" does not fundamentally change the original material except perhaps to reshape it or put it in another form.
As such, "glass" is made FROM sand (est fait à partir de sable), but not made OF sand (n'est pas en sable). HTH
"à partir de" means "starting from", "based on". The thing that follows is something that was used as a starting place, as a place of origin, but is not itself present anymore in its original form.
In short, it applies to a source of some thing while not being that thing itself. (Glass isn't sand anymore, but golden car essentially still is/contains gold.)
(Replace "de" with "du" or "des" to get different examples.)
As you can see, the object of the phrase can be pretty much anything: a thing, time, place, process. The French verb "partir" implies that there was something left behind. Think of the difference between "made of" and "made out of".