Philippinites, or rizalites are tektites found in the Philippines. They are considered to be about 710,000 years old on the average[1] and generally ranging in size from millimeters to centimeters.[2] Their age corresponds with the age of other tektites in the Australian strewn tektite field. In 1964, a very large philippinite, weighing 226.3g with dimensions 6.5 x 6.2 x 5.2 cm, was purchased by the University of California, Los Angeles Department of Astronomy.[3] The heaviest philippinite ever found weighs 1281.89g in its splash-form, which is also the heaviest tektite of this kind.[4]
The term rizalite was named after the Philippine province of Rizal where the first black tektites were rediscovered in October 1926 at Novaliches (which was then part of Rizal).[5] Although, it was only in 1928 that the term was proposed by American anthropologist H. Otley Beyer, dubbed as the father of Philippine tektite studies, to refer to tektites found in the Philippines.[6] Philippinite has become the more favored term because other tektites were found in other areas of the Philippines such as the Bicol region and the town of Anda in the province of Pangasinan.[7] Some early authors referred to Philippine tektites as "obsidianites" but that too has fallen out of use due to the introduction of the term philippinite by succeeding authors.
In ancient Philippines, tektites were used by early settlers in the Philippines as arrowheads and other tools as well as decorative purposes. During the Philippine Iron Age, due to the polish features of philippinites found in graves, it was evidenced that philippinites were used as amulets or charms.[8] In modern times, it is generally used as a collector's item.
The following table details the chemical composition of philippinite:[5]
| Oxides | Content (in weight percentage) | Number of determinations | |
|---|---|---|---|
| SiO2 | 70.66-71.64 | 4 | |
| TiO2 | 0.63-1.04 | 4 | |
| Al2O3 | 12.08-13.52 | 4 | |
| Fe2O3 | 0.59-2.03 | 3 | |
| FeO | 3.03-5.32 | 4 | |
| MnO | 0.08-0.16 | 4 | |
| CaO | 2.95-3.42 | 4 | |
| MgO | 2.23-3.65 | 4 | |
| Na2O | 1.21-1.66 | 4 | |
| K2O | 1.69-2.28 | 4 | |
| H2O+ | 0.15-0.63 | 4 | |
| H2O− | Traces | 1 | |
| P2O5 | 0.10-0.18 | 3 |