Congrats on rescuing this little guy....as far as soil goes, check any one of the THOUSAND of threads on this very forum for C&S potting mixes.....Definately , the more light , the better, mine seem to thrive in direct sunlight spring through fall....those little piece WILL come off with very little effort, just stick them in the soil, and more times than not, they will indeed take root on their own...I'm sure there may be some who say "let them root first" but, i believe that the easy breakage and rooting is a " survival thing" for the plant , and no one plants them after they've rooted in the wild....lol
As far as terrariums go, i cannot answer a I have NO experience, i DO know that they make a great addition to a dish garden.....if there's anything I've missed, or, that someone feels needs amending, stick around...these are great folk here , and they will answer ! Good Luck !
Jay

I didn't catch the terrarium question. No. Never. Nein. Non. Absolutely not. Terrariums are still and have no drain.

Almost all desert cacti benefit from a fan. No, not the Jeff Harris kind of fan of desert cacti. He will not go to your home and move the air around. (Although many cacti do benefit from fans like him.) A circulating fan. Anything less than good air circulation and you risk arrest from the same plant police.

hmmmm would have sworn it was "mammilaria gracilis fragilis"

Mammillaria vetula v. gracilis, said between guffaws.

Jeff,
It's been a very long day for me and I'm tired and have no idea where Webster ran off too..lol.. so .. :-)

What does guffaws mean? :-)

I have "mammilaria gracilis fragilis". What is the difference between it and "Mammillaria vetula v. gracilis", Is it the longer thorns I see in the pic above?
from the google I did on the two plants, that is about the only difference I can see. Haven't had a chance to read up on the 2.

JoJo

From the Free Dictionary, JoJo:

n. A hearty, boisterous burst of laughter. intr.v. guf�fawed, guf�faw�ing, guf�faws. To laugh heartily and boisterously.

I don't know the difference between those two.

LOL!
Thanks Jeff.. I forget about the free one!

JoJo

this plants commonly marked as fragilis by all the growers that manage to get there plants over here to the east coast, I for one always thought it to be about the most logical name for a plant, so then its probably not fragilis...what ever, they are nice litle plants but best left in a spot they like and dont need moving.

answers
1 too much peat! it wont take water when its dry, and that plant wants to be dry at times...
2 thouroghly watered...is not a measured amount, the dirt needs to be watered until moist, all the way through, usually soaking for an hour in an inch of water will do it
3 that soil has too much dust and tiny particles, not enough large chunks, and it all absorbent, it needs sand, gravel pumice,pebbles, fired clay, something that will not soak up water, it helps it all dry out fats and even after a good thorough watering : D
4 those are now cuttings, dont water tem until they have roots, you will need to anchor them to the dirt, they will float away if you water from about, or even roll in the wind, or when moved.
5 sure why not, it wont be ideal, and the is a big diffence between thriving and surviving but they can certainly survive a dry open artificially encloser. Realisticly, it doesnt sound like you know enough to really make a great cactus terrarium but you can certainly try.

goodluck

Jeff, on the guffaw aside question, the difference is one is a verb and one is a noun.