SPHERULITES, in petrology, small rounded bodies which commonly occur in vitreous igneous rocks. They are often visi ble in specimens of obsidian, pitchstone and rhyolite as globules about the size of millet seed, with a duller lustre than the sur rounding glassy base of the rock, and when they are examined with a lens they prove to have a radiate fibrous structure. Under the microscope the spherulites are of circular outline and corn posed of thin divergent fibres, which are crystalline and react on polarized light. Between crossed nicols a black cross appears in the spherulite ; its axes are usually perpendicular to one another and parallel to the crossed wires; as the stage is rotated the cross remains steady; between the black arms there are four bright sec tors. This shows that the spherulite consists of radiate doubly refracting fibres which have a straight extinction ; the arms of the black cross correspond to those fibres which are extinguished. The aggregate is too fine grained for us to determine its minerals.
Spherulites are commonest in acid glassy rocks but occur also in basic glasses such as tachylyte. Sometimes they compose the whole mass; more usually they are surrounded by a glassy or felsitic base. When obsidians are devitrified the spherulites are often traceable, though they may be more or less completely re crystallized or silicified. In the centre of a spherulite there may be a crystal (e.g., quartz or felspar) or sometimes a cavity. Oc casionally spherulites have zones of different colours, and while most .frequently spherical they may be polygonal, or irregular in outline. In some New Zealand rhyolites the spherulites send branching "cervicorn" processes (like stags' horns) outwards through the surrounding glass of the rock. Long, elliptical or band-like spherulites are called axiolites.
Spherulites may be fin. or more in diameter. In composition they are a mixture of quartz and acid felspar.
Very large and cavernous spherulites have been called litho physae; they are found in obsidians at Lipari, the Yellowstone Park, etc. The characteristic radiate fibrous structure is usually conspicuous, but the fibres are interrupted by cavities which are often so arranged as to give the spherulite a resemblance to a rosebud with folded petals separated by arching interspaces. Some
of these lithophysae are 'in. or more in diameter. In the crys tallization of a glass there must be contraction, and it is supposed that thus the concentric cavities arise. The steam and other va pours in the magma would fill these empty spaces and exert a pow erful mineralizing action on the warm rock. Analogous structures may be produced in artificial glasses, salt solutions and melts of organic substances. ( J. S. F.) SPHINX, the Greek name for a compound creature with lion's body and human head (Gr. o-c/Aryetv to draw tight, squeeze). The Greek sphinx had wings and female bust, and the male sphinx of Egypt (wingless) is distinguished as "andro sphinx" by Herodotus. The type perhaps originated in Egypt, where a defined type is usually recumbent. The most celebrated example is the Great Sphinx of Giza, 189ft. long, a rock carved into this shape, and from its situation likely to be the work of the IVth Dynasty.
According to inscriptions of the XVIIIth Dynasty in the shrine between the paws, it represented the sun god Harmachis. It has recently been completely excavated and its head restored. Sphinxes of granite, etc., occur of the XIIth Dynasty and later. (See EGYPT, Art and Archaeology.) The heads of the sphinxes are royal portraits, and apparently they are intended to represent the power of the reigning Pharaoh. The king as a sphinx, in cer tain religious scenes, makes offerings to deities; and elsewhere he tears his enemies in pieces. Sphinxes in pairs guarded the approach to a temple, and the Great Sphinx at Giza so guards the entrance of the Nile valley.
The great temple avenues at Thebes are lined with recumbent rams, true sphinxes (a few late instances), and with the so-called criosphinxes or ram-sphinxes, having lion bodies and heads of the sacred animal of Ammon. A falcon-headed sphinx was dedicated to Harmachis in the temple of Abu Simbel, and is occasionally found in sculptures representing the king as Horus, or Mont, the war-god. It is distinguishable from the gryphon only by the ab sence of wings.