This is "The Green Book", a 1986 novel by Jill Paton Walsh
It features crystalline plants (which you can see on the book cover) and a starvation theme;
Refugees from the dying planet Earth, they, along with
other ships, have been sent into space in the hope that some of them
will survive to continue the human race. But the success of Shine
remains doubtful as crops fail and provisions brought from Earth
Even the excitement surrounding the hatching of the giant
moth people from the "boulders" in Boulder Valley doesn't make the
group forget the hopelessness of the situation. It isn't until Pattie
and her sister Sarah make an important discovery that survival becomes
The book contains a couple of quite vivid descriptions of the vegetation:
One morning when we woke up they were all sick, lying in a heap in a
corner of their hutch, with sad cloudy eyes. And by the next day they
were all dead. Sarah said they died of homesickness; Father thought
they might have caught some kind of virus; most people thought they
had been killed by eating the crystalline plants. The chickens were
all right; and they had eaten only Earth-grown grain.
Eventually, the children realise that despite the grains being like glass beads, they can be crushed and ground like flour:
But Sarah said, "I'm going to try, I'm going to try, I'm going to
try!" She stole a handful of the glass beads, and rubbed them between
two stones, and they fell easily into a dry white powder that smelled
good. She sent Pattie for a ladle of lake water, and mixed a dough,
and rolled it out thin, and made a pancake, and cooked it on the fire.
Then, when it looked done, she broke it into four pieces, and gave one
to Pattie and one to Joe, and bit into one herself, leaving Father's
share in the pan.
Oh, it tasted good! We ate it in three bites.