Spherulitic Jaspilite from Whangarei Heads By A. M. Hopgood [Received by Editor, October 15, 1956.] Abstract Spherulitic jaspilite occurring in small lenses at McLeod Bay, Whangarei Heads, is closely associated with fine-grained spilitic rocks. Individual spherulites within the jaspilite exhibit both concentric and radial form and show crowding of haematite and minute silica particles into concentric zones. The location of the Jaspilite as xenoliths within spilite indicates that banded haematitic cherts caught up by the spilite have been partially dissolved and re-crystallized to their present spherulitic form. Introduction At the west end of the north side of McLeod Bay, Whangarei Heads, greywacke sandstones are associated with limestones, igneous rocks, and red spherulitic jasperoid cherts (Fig. 1). These rocks have been mapped by Allen (1951) as part of the basement (Trias-Jura?) Waipapa Series. However, neither Allen nor Bartrum (1948) mentions the igneous rocks associated with the cherts, although a description of an altered tuff from near this locality is to be found in Allen's (1951) account. The jaspilites occur in the shore platform just below high water mark about half a mile east of the mouth of Parua Bay. The outcrop lies between two limburgite flows, a quarter-mile apart, which are described by Allen (1951). Allen (1947) states, “The writer believes, then, that the radial structures in the spherulitic jaspilite were developed by slow crystallization along with haematite (or its precursor) in open cavities where colloform structures are of normal occurrence. The problem as to whether or not hydrothermal waters played a part in the silicification is a difficult one, for evidence is not readily forthcoming.” This problem, as well as that posed by the occurrence of non-spherulitic jaspilites from other localities in the area, is overcome by the discovery by the writer of igneous rocks intimately associated with the jaspilites. Field Occurrence The jaspilites are found in spilite as xenolithic pockets and lenses, up to 5 inches deep, which give the appearance of having been folded into the enclosing black and green igneous rock. Individual spherulites within the jaspilite reach diameters of up to a quarter inch and range from dark reddish-brown to colourless. The sharp boundary of the haematite matrix of the jaspilite against the enclosing intrusives serves to accentuate the “rolled-up” appearance of the lenses. Weathering has produced on the jaspilite a pisolitic surface which stands out in marked contrast to the angular pattern etched on the surrounding greywacke. Small patches of iron pyrites are scattered throughout the jaspilites, and both jaspilites and spilite are seamed by an irregular network of veins of crystalline quartz and calcite. Petrography Jaspilite According to Pettijohn (1949) the term spherulite is applied to oolitic bodies “in which, however, only radial structure is visible.” The structures described here are both radial and concentric and therefore fit the definition of oolites as well as spherulites. However, in many cases they have irregular outlines, indicating growth in a solid medium in the manner advocated for spherulite formation by Pettijohn (1949).