{To look upon} (horasei). Locative case of horasis, old
word (from hora(935c), to see) for appearance (in appearance) as in
 Eze 1:5,26 . {Like a jasper stone} (homoios iaspidi).
Associative-instrumental case of iaspis, old word (Persian),
used for stones of different colors, one opaque like opal, one
translucent ( 21:11,18f. , possibly here, only N.T. examples),
one a red or yellow stone ( Isa 54:12 ). Some even take it for
the diamond. Certainly not our cheap modern jasper. {A sardius}
(sardi(9369)). Old word, in N.T. only here and  21:20 . The
carnelian or other red stone, derived from Sardis (Pliny).
{Rainbow} (iris). Old word, in N.T. only here and  10:1 . From
 Eze 1:28 . {An emerald} (smaragdin(9369)). Adjective (from
smaragdos,  Re 21:19 ), of emerald (supply lith(9369)), in
associative instrumental case after homoios. John sees no form
for God ( Ex 24:10 ), but only the brilliant flashing gems. "In
the vision the flashing lustre of the iaspis and the fiery red
of the sard are relieved by the halo (iris) of emerald which
encircled the Throne" (Swete). A complete circle.