As Green As Emerald

Ancient Mariner, of course:

And now there came both mist and snow,
And it grew wondrous cold:
And ice, mast-high, came floating by,
As green as emerald. [lines 51-54]

Why green, though? Icebergs are white, as any fule kno. Ah, but Coleridge had never seen one with his own eyes. His sense of what an iceberg was, I now realise, came not just from books but from a particular book: David Crantz's two-volume History of Greenland (1767). We know Coleridge read this work because he makes reference to it in a footnote to ‘Destiny of Nations’, by way of explicating the famous ‘Wizard of Greenland’ passage (lines 98-112) from that poem. ‘Destiny’ was originally part of Southey's Joan of Arc (1796), and was republished as a Coleridge-only standalone in Sybilline Leaves (1817). Here's the relevant bit:

So: Coleridge was reading Crantz's History of Greenland in the mid-1790s, which is to say in the run-up to writing Ancient Mariner. And what does Crantz have to say about icebergs? I'm glad you asked:

So that's where STC's green icebergs come from!

And actually this context gives us new information regarding the poem. Perhaps we think of the phantasmagoric landscapes (or seascapes) through which the mariner travels as old, in some sense; importing ancientness from protagonist to environment—I suppose because his adventures seem like a personal psychodrama projected outward onto the big screen of the world. But maybe that's not what's going on here. When the mariner enters the land of mist and snow, he is entering a new world, with fresh-minted ice (not, so far as Coleridge believed, older, melted-and-refrozen bergs). That's interesting, I think.