It has occurred to me, that you possibly might like to see the specimen of obsidian & some curious, most finely, laminated obsidians & trachytic rocks, which I collected at Ascension island. You would not of course, I presume, think it worth the expence of carriage to have the specimens sent to Edinburgh; but shd you at any time come to London, I should be proud, if you so like, to send them for your inspection. If the subject of the lamination of volcanic rocks should interest you, I would venture to ask you to refer to p. 65-72 of my small volume, Geolog: Obser: on Volcanic Isl. which would be in the Public Library. I there throw out the idea, that the structure in question may, perhaps, be explained by your views on the zoned structure of glacier-ice: the layers of less tension, I may add, being in the case of the Ascension Obsidian-rocks, rendered apparent chiefly by the crystalline & concretionary action superinduced in them, instead of as in your ice, by the congelation of water.

Charles Darwin in his correspondence to James Davis Forbes dated 11 October (1844)

Atlantic Obsidian Sources

ASCENSION ISLAND | CANARY ISLANDS | ICELAND

OBSIDIAN SOURCE NAME ALTERNATE SOURCE NAMES
ASCENSION ISLAND
Ascension Island --
CANARY ISLANDS
San Miguel Island --
Tenerife --
ICELAND
Hágöngur --
Hraftnunruggen --
Hrafntinnuhraun --
Katla --
Kerlingarfjöll --
Krafla --
Kviarjokull A --
Kviarjokull B --
Landmannalaugar --
Torfajökull --

IAOS SOURCE CATALOG
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Last Updated: 04/09/2016
International Association for Obsidian Studies