The Lava Flow of the Crater of Kilauea, Hawaiian Islands
From a Stereograph, Copyright, by Underwood & Underwood
Fragments of lava that possess a cellular structure form what are known as scoriæ. The lightest of all kinds of scoriæ is what is known as thread-lace scoriæ. Here the thin walls consist of mere threads. [Figs. 26] and [27] represent the appearance of thread-lace scoriæ from Kilauea. The separate threads are very fine, being only from one-thirtieth to one-fortieth of an inch in thickness. As can be seen, this form of scoriæ have six-sided or hexagonal shapes. You can form some idea of the great lightness of such scoriæ when you learn that they contain only 1.7% of rocky material. Indeed, they contain so little solid material that a layer of volcanic glass only one inch thick, if blown out into scoriæ, would be able to produce a layer sixty inches thick.
Fig. 26. Thread-lace Scoriæ from Kilauea
From Dana's Manual of Geology
Another curious form sometimes assumed by lava, especially in the case of Kilauea, is where the lava is spun out in the form of long silk-like hairs. This is called by the natives Pele's hair, after the name of their goddess. Inasmuch as the origin of this form of lava was at one time generally attributed to the action of the wind in drawing out thread-like pieces from the jets of lava thrown upwards from the pool, it will be interesting if its true cause is explained.
Fig. 27. Thread-lace Scoriæ from Kilauea
From Dana's Manual of Geology