Many thanks for the comments and responses !

The Japanese pendant sounds beautiful, but I am sure this is not the
same type of material as Mekhaphat.

Meteorite fragments are sometimes used in several forms in the religious
arcana of the "animist universe" that swirls around the
formal traditions of Theravada Thai Buddhism like moths around a flame.
Meteorite fragments are referred to in Thai as "dao tok"
which translates as "fallen star." Meteorite is considered specially
"magically potent" in making "takut," fetishes worn usually on
a braided belt believed to protect from harm in battle.

I am not familiar with hypervelocity impact produced tektites, but will
pursue this line of inquiry. Lodestone or hematite are also
good hypotheses to be pursued.

Mekhaphat (and its rarer cousin "mekhasit") await clarification.
Whatever it is, it is hard enough and strong enough to take
detailed carving as a beautiful Cambodian piece of a Buddha surrounded
by two phiyanaag (primordial water serpents who look a lot
like Chinese dragons) in my collection attests. A local dealer has a
Phra Sangakajai (fat Monk often mistaken for the fat Buddha
coming from the Chinese Mahayana tradition) he claims has a coating of
mekhapat over bronze : if that is true, then it was
definitely cast which means it is definitely meltable and pourable. This
material though looks porous and smells of sulfur; the
mekhapat I have seen is almost always semi-gloss (artifact of polishing)
appears non-porous and has no distinct odor.

If I find a really "definitive" answer, I will post either a summary or
a link on this group.

Sawasdee Khrup, Bill Woodruff
Chiang Mai, Thailand