The manna was as coriander seed. On the name and the nature of the manna see Exodus 16:31. It is commonly supposed that the brief description here inserted was intended to show the unreasonableness of the popular complaints.
There is no trace whatever of any such purpose. So far as the description conveys fresh information, it was simply suggested by the occurrence of the word "manna," according to the artless style of the narrative.
If any moral purpose must be assigned to this digression, it would rather be to suggest that the people had some real temptation to complain. It is often forgotten that, although the manna was supernatural, at least as to the amount and regularity of its supply, yet as an article of food it contained no supernatural elements.
If we had to live upon nothing but cakes flavored with honey or with olive oil, it is certain that we should soon find them pall upon our appetite. To the eye of the Psalmist the manna appeared as angels' food (Psalms 78:25); but then the Psalmist had not lived on manna every day for a year.
We have to remember, in this as in many other cases, that the Israelites would not be "our ensamples" ( τύποι ἡμῶν, 1 Corinthians 10:6) if they had not succumbed to real temptations. As the colour of bdellium.
See on Genesis 2:12. As no one knows anything at all about bdellium, this adds nothing to our knowledge of the manna. The Septuagint has here εἷδος κρυστάλλου, "the appearance of ice," or perhaps "of hoar-frost."
As it translates bdellium in Genesis 2:12 by ἄνθραξ (carbuncle), it is probable that the comparison to ice here is due to some tradition about the manna. Taking this passage in connection with Exodus 16:1-36:81, we may reasonably conjecture that it was of an opalescent white, the same colour probably which is mentioned in connection with manna in Revelation 2:17.