I've never heard of methadone 'crystals'. I would be concerned you have something else.
That being said, if you do not have a very high opiate tolerane you may want to pass on this, and even with one be very, very careful. Methadone is one of the most likely opioids to cause an OD.
It is deceptivey powerful, if you really do have pure methadone then you need a milligram scale unless your opiate tolerance is huge. If you don't have a tolerance you are likely to end up dead before you finish your stash.
If you have experience with opiates chances are you could still end up ODing, has methadone is not very euphoric, and people who are used to oxy or heroin will keep taking more and more and more chasing that classic opiate feeling that will never come, this combined with methadone LONG time to peark and long half life WILL lead to OD. It can take 6+ hours for methadone to peak, so you need to not redose before then. Thats how it gets you, people take it, don't get the high they are expectin, take more an hour later, still don't feel "high" take more 2 hours later, then before they know it you are on the ground, and it ain't like a heroin OD, with mdone you are NOT waking up withou narcan, you will be dead.