There is at least one other option.
From talk.origins

Fortunately in Forbidden Archeology by Michael
Cremo and Richard Thompson, some additional information
is given. First, it states:

Over the past several decades, South African miners have
found hundreds of metallic spheres, at least one of which has
three parallel grooves running around its equator. The spheres
are of two types--"one of solid bluish metal with white flecks,
and another which is a hollow ball filled with a white spongy
center" (Jimison 1982).

It is important to note at this time, that (Jimison 1982) is:
Jimison, S. (1982) Scientists baffled by space sph...

There is at least one other option.
From talk.origins

Fortunately in Forbidden Archeology by Michael
Cremo and Richard Thompson, some additional information
is given. First, it states:

Over the past several decades, South African miners have
found hundreds of metallic spheres, at least one of which has
three parallel grooves running around its equator. The spheres
are of two types--"one of solid bluish metal with white flecks,
and another which is a hollow ball filled with a white spongy
center" (Jimison 1982).

It is important to note at this time, that (Jimison 1982) is:
Jimison, S. (1982) Scientists baffled by space spheres. Weekly
World News, July 27.

A citation chain that ends at the Weekly World News doesn't exactly make me want to drop everything.

Wikipedia has a summary (at least as of this date).

"Research carried out on several crystal skulls by the British Museum
in 1996 has shown that the indented lines marking the teeth (for this
skull has no separate jawbone, unlike the Mitchell-Hedges skull) were
carved using jeweler's equipment (rotary tools) developed in the 19th century, making a supposed pre-Columbian
origin even more dubious. The type of (rather poor quality) crystal is
Brazilian, and unknown within the Aztec or Maya territories. The study
concluded that the skulls were crafted in the 19th century in Germany.
A similar research carried out by the Smithsonian Institut...

Wikipedia has a summary (at least as of this date).

"Research carried out on several crystal skulls by the British Museum
in 1996 has shown that the indented lines marking the teeth (for this
skull has no separate jawbone, unlike the Mitchell-Hedges skull) were
carved using jeweler's equipment (rotary tools) developed in the 19th century, making a supposed pre-Columbian
origin even more dubious. The type of (rather poor quality) crystal is
Brazilian, and unknown within the Aztec or Maya territories. The study
concluded that the skulls were crafted in the 19th century in Germany.
A similar research carried out by the Smithsonian Institution in 1992 on a crystal skull provided by an anonymous source who claimed to have purchased it in Mexico City in 1960 and that it was of Aztec
origin concluded that it, too, was made in recent ages and that it
originated with Eugène Boban, a French collector of pre-Columbian
artifacts and antiques dealer who ran his business in Mexico City
between 1860 and 1880. According to the Smithsonian, Boban acquired the
crystal skulls he sold from sources in Germany; findings that are in
keeping with those of the British Museum.
Mitchell-Hedges mentioned the skull in the first edition of his autobiography, Danger My Ally
(1954), without specifying where or by whom it was found. He merely
stated that "it is at least 3,600 years old and according to legend was
used by the High Priest of the Maya when performing esoteric rites. It
is said that when he willed death with the help of the skull, death
invariably followed". Later editions of Danger My Ally omitted the skull entirely."