There are plenty of sandy beaches in Japan. As to the chemical composition of the sand, this piece suggests that there's quite a bit of silicone dioxide in the form of quartz dust - but perhaps the impurities make it difficult to refine for glassmaking?http://sciencelinks.jp/j-east/article/200322/000020032203A0746666.php
These authors would know quite a bit about the composition of sand in Japan - maybe you could email them?
Other useful link: History of Glassmaking in Japan:http://www.engravedglass.cz/lectures/3pred_takeda_en.html
According to this, in the mid-1800s, the Japanese had just started to move into automated glassmaking.
Just thinking, perhaps it has nothing to do with the sand. Maybe the earliest attempts at sheet glass were disasterous, the factories lost huge amounts of money, and so they had to move quickly into something more profitable before they folded.
I only suggest this because when the Australian glass manufacturer AGM moved into window glass in the 1930s, their first attempts were woeful (there are files full of complaints). If they hadn't been able to heavy the government to increase tariffs and rely on profits from their bottlemaking arm, I wonder whether they would have had to give up.
And now an anecdote about Japanese sand! Back in 1988, the Canberra Youth Orchestra Wind Ensemble were invited to a band festival in Shizuoka, Japan. Being organised by the locals, our movements had been planned to the slightest detail. We were told we had to stay in a stuffy, inner room without windows for three hours to 'tune up', with any stray escapee rounded up and shepherded back by our stern Japanese minders. Perhaps this was a comment on our musicianship?
After a week and a half of seeing more of the insides of schools than exploring Japan, we were frustrated, and so we whined and cajouled our minders to take us to a beach. They finally gave in, and we gathered our togs and towels and were driven to a nearby coastal area, Miho no Matsubara. My pictures from the day show a bunch of plump, white, teenagers standing on jet black sand, staring dejectedly out into a completely surfless beach on an overcast day. We'd been warned the water was too dangerous to swim in. That Mount Fuji was allegedly somewhere behind the mist made little difference. We did, however, see a very old tree, braced up with planks, on which "some mermaid had dumped her clothes", to quote a friend. Thinking back now, I'm embarrassed at how insular and self-centred we were. Here was a place of real significance, and yet we were disappointed because it didn't look like a standard Aussie beach. That black sand just seemed to sum up our feelings about the trip. http://en.wikipedia.org/wiki/Miho_no_Matsubara
Luckily, we did get to do a little sightseeing after the convention had ended, including a cheery jaunt to the museum at the epicentre of the Hiroshima blast. [No Nukes!]