In August 2014, I purchased a tektite from my friend, Norm Lehrman. It was a 137 gram Rizalite tektite. Norm enclosed a letter with my tektite. I bought the tektite because it was transitional and instructive. In the letter, Norm wrote, “You might appreciate a note explaining why I termed the 137.0 gram Rizalite “Instructive”. Philippinites are noted for several peculiar morphologies. These include the spheres, sometimes heavily ornamented to form soccerballs, and sometimes bald. The classic Rizalite form is characterized by concave-convex flakes with deep ornamentation on the convex side and a smooth concave surface. The “bald” sphereoids form when the heavily ornamented skin spalls off, forming the concavo-convex flakes. This 137.0 gm specimen is transitional between a heavily ornamented soccerball, and a bald sphereoid. Several “Bikolite” flakes have popped off, leaving low relief bald spots at the detachment surfaces.”
Norm goes on to explain that “Rizalite” and “Bikolite” are terms referring to specimens recovered from particular areas – Rizal province and Bikol Peninsula, Philippines.
I was curious and wondered when Rizalites or Bikolites become bald, so I asked my friend, Aubrey Whymark, at what weight this occurred. Without mentioning Norm’s name, I told Aubrey about Norm’s hypothesis. Aubrey disagreed with his theory.
Aubrey hypothesized, “Large Philippinites are not smooth due to shell loss. They are smooth because they retained sufficient heat on re-entry to avoid brittle failure. Therefore you never see these polygonal fractures on large specimens except rarely on bubble specimens. Below around 350 g they cooled sufficiently prior to re-entry such that they could be heated then cooled during re-entry forming polygonal cracks and shell loss. Shell loss only occurs on smaller specimens. No shell loss on larger specimens. Also theoretically no shell loss on small few gram Philippinites (but these do not survive).” “You will never find a large sphere with attached shell because they never had a shell. The odd large specimens with shell are clearly bubble fragments. As they did not form large solid sphere they cooled quicker like breadcrusts and formed polygons on re-entry. You need to calculate cooling time and flight time. You will see that large spheres where too hot for brittle failure during re-entry. So breadcrust are paper-thin polygonal cracks on an unoriented body that enters the atmosphere cool. It heats up and then cools during re-entry and then cracks high up in the atmosphere. Shells may be lost. The largest tektites appear to be too hot during re-entry (a large body with a lower surface area to volume ratio stays hot much longer). It also heats up but then will not crack as it is still hot. As they cool further they are liable to fragment (less so if they contain a bubble). Any shell loss is thin spalls similar to Indochinites that entered hot.”
I respect both Norm and Aubrey. They both have similar backgrounds – they are both geologists with many years of experience, have collected and studied Tektites for many years, and both love Tektites. Over the years, I have gone to one or the other or both with questions about Tektites. I consider both of them to be my Tektite mentors. I wanted to express both Norm and Aubrey’s theories, and let the readers ponder them before they come to their own conclusions.
Jim and Paul congratulations on twenty years of bringing the meteorite community knowledge, entertainment and friendship through Meteorite Times!