'Dark' in the Bible

And [so] you came near, and you stood under the mountain, and the mountain [was] burning with fire up to the heart of the heaven, {dark with a very thick cloud}.

And you shall be groping at noon just as the blind person gropes in the dark, and you shall not succeed [in finding] your way, and you shall only be abused and robbed {all the time}, and there will not be {anyone who will rescue you}.