Revelation 4:3

a jasper and a sardine stone Our jasper, a stone the colour of which varies between red, green and yellow, does not seem very appropriate to the image here, nor to answer to the description in Revelation 21:11, as it is not sparkling nor transparent. But it seems proved that the jasper of the ancients (the word is substantially the same in Hebrew, in Greek and Latin, and in modern languages) was the translucent stone now known as Chalcedony especially the green variety. The sardius (so we should read) is certainly the choicest kind of red carnelian, translucent and fiery in colour, but not exactly sparkling.

round about the throne i.e. forming an arch over it.

in sight The word is the same as "to look upon" just before, though the construction is somewhat varied.

like unto an emerald Here there is no doubt what stone is meant: we have only the question whether the rainbow was allgreen, or only produced the same effect on the eye as an emerald brilliant yet not dazzling. The ancients felt very strongly the relief given to the eye by looking at it. The rainbow in any case no doubt represents God's revelation by a covenant of grace, Genesis 9:13 sqq.