Thank you to all! I also did an web search last night and discovered that cracking cast iron isn't all that uncommon - mostly when heat and cold are too quickly applied. So I will pre-heat more slowly in the future. I cook a lot - and I'm still getting used to cooking with induction. Boiling water - as the expression goes - is the best and easiest. Sauteeing, I have discovered, has a learning curve, depending on the pan (I have several, some old LeCrueset, some expensive DeMeyere, some cheap made-for-induction). The best are enameled cast iron, i.e. LeCrueset or Descoware. I had purchased an inexpensive griddle which I ended up throwing away - it buzzed, it burned food, it was hard to clean. I replaced it with the cast iron griddle, which arrived in the mail poorly packed, with a chip on the rim. I should have sent it back - it was not inexpensive - but I figured it was still cooking-worthy and return shipping was a fortune. That chip on the rim may have compromised the pan enough to crack it. It was also too large for the hob - 14" on a 12" circle. That may have contributed to the problem. The next one I buy - I haven't given up - will be smaller. I will pre-heat it more slowly. On my old electric stove, I set my former non-stick griddle (not induction compatible, so I gave it away) on the high setting, let it heat up, turned down the heat, and made perfect pancakes every time. The adventure continues!

Seems normal to me. What is above the burner will be heated by induction. After that it is conduction towards the pan edges. It's not particular to cast iron but to any ferromagnetic pot/pan.

Yes. The field that activates the ferrous material goes a bit beyond the surface of the cooktop. The distance is very slight and shouldn't make a difference. There is a caveat to using CI on induction. It is terrible at conducting heat and you'll notice hot spots. It's very slow to come up to temp, or changing temp, and doesn't utilize the wonderful responsiveness that induction can offer. You'll want cookware with aluminum or copper cores to reap the best out of your cooktop. Not sure if you wanted to use CI exclusively, but I thought I'd address it for future readers. I'm not anti CI. I have a 10 inch skillet that I like for certain things and for use in the oven, as well as a couple of enameled dutch ovens.

Scratching, chipping, etc of smootop surfaces? Lots of prior discussions of this here including this one which, for anyone interested, has links to many other earlier postings on the subject. http://ths.gardenweb.com/discussions/2346300/causing-scratches-breakages-on-induction-cooktop >>>"the air between the pan and the glass can get very hot . . . accidents and burns when it escapes . . . cracking of the glass"<<< I don't mean the following as an attack on plllog. I, too, have seen some of the alarmist warnings that plllog describes where folks tell you what you are "supposed" to do or not do and what are the risks with induction. First, on the casting rings maybe causing problems with the pan-recognition sensors, that does not seem to be the case with skillets. Those rings are just not thick enough to elevate the pans enough to cause any problems. Where I've seen reports of problems has been with some cooktops and those reversible griddle-grill pans. (You know what I'm talking about -- the pans with smooth pancake griddle on one face and a ridged/rippled grill surface on the other?) Some brands of those reversible pans apparently had or have a very high lip on the "grill" side and the lip was high enough that when the griddle side was up (and the grill side was down) the lift was high enough to have confused the pan sensors on some induction cooktop a number of years ago. Last time I recall seeing a report of this problem was maybe four years ago. (Actually, IIRC, it might have been plllog who found that report.) Anyway, that grill-pan's lips were much taller than the casting rings on the skillets the OP was concerned about. Beyond that, I put the other kinds of warnings in the same category as other earnestly fearful but uninformed posts about induction. Fr'instance, I've seen any number of posters insisting that some European commission has determined that induction actually uses non-ionizing radiation to heat the foods and it is heating the food that heats the pans, destroys nutrients and adversely affects health. Other earnestly fearful posters have insisted that you must only use wooden spoons and such with induction because using steel utensils will somehow electrocute you. As for cracking, you obviously might crack a smoothtop by dropping a 7 quart, cast iron dutch oven full of water/soup/whatever several feet down onto any smoothtop ... well, you get the idea. The other stories about cracking surfaces actually originate in situations that have nothing to do with cast iron skillets, one about vacuum suction and the other about thermal shock. The "vaccum" suction theory might be be extrapolated from reports about folks pulling a large, hot, steamy domed pot lid off a pan, immediately plonking the lid rim-side down on the smooth surface. If the lid is large enough and the rim is perfectly straight, if there is enough steam trapped and the lid cools quickly enough, then a vacuum can develop. Large-enough lids apparently have produced sufficiently strong suction to have cracked a smoothop. There is just not enough room under any cast iron skillet for this to occur and it is unikely you could have enough liquid under it, either, without the burner shutting down and throwing an error code. The idea of cracking caused by "thermal shock" really has nothing to do with cast iron pans, either. Most of the reports that I have seen about thermal shock cracks have been with ultra-cheap portable induction cookers (PICs) that cut costs by using thin, tempered glass tops rather Schott "Ceran," the heavy duty glass-ceramic used on better PICs not to mention all smoothtop/induction ranges and cooktops. Ceran is designed to withstand thermal differentials of at least 750° F. Anybody heating pans that hot on induction has tampered with the control circuits & programming and is engaged in industrial metal smelting, not cooking. Other than that, Schott's products are mass produced and, like all mass produced products, there will be some tops with manufacturing defects that will break under use. That's a manufacturing problem, not a cast iron problem. As for superheated air burning cast iron users, again, there just is not enough air space under a cast iron pan and casting rings are never perfect enough for that to be a real problem, anyway.