The occasion of Spock's mother's passing is described in great detail in the TOS novel "The Fire and the Rose":
Beneath the fiery sky, on the plain of Vel’Sor, in the land held by
his family for more than thirty generations, Sarek let go of Amanda.
He stood at the center of the megalithic structure, atop a low
platform, beside a circle of burning coals that represented so much:
his wife’s lost katra, their connection to each other, their life
together. Even now, thirteen days after the shuttle crash that had
taken her from him, after confirmation that she had indeed been aboard
the doomed craft, Sarek battled his emotions with his logic, and he
did not always win. In his many years, he had never faced a more
difficult challenge.
Silently, he gazed about the circular grounds, at the dozen members of
his extended family who had come here today and who now ringed the
periphery of this ancient place. Behind them, red granite pillars rose
out of the hard soil, topped by horizontal slabs of stone. The breeze
blew hot here, the air a furnace even by Vulcan standards. The chimes
scattered around the structure infused the environs with a continuous
peal.
“What we have experienced here today,” Sarek said, his voice sounding
stronger than he felt, “has come down from the time of the beginning,
without change.” He addressed all of those present, but as he had for
most of the long ceremony, he peered into the steady gaze of T’Pau.
“This is the Vulcan heart. This is the Vulcan soul. This is our way.”
Sarek bent and hefted the large ewer that sat beside the bed of
white-hot coals, the searing temperature nearly blistering the flesh
of his arms. Holding the antique container away from his body, he
angled it downward. Water spilled from its mouth into the pit. The
coals hissed as they drowned, gushing clouds of white steam rising
upward. Sarek poured until he upended the ewer. Then, its contents
spent, he set it back down.
“As it was at the time of the beginning,” he said, “so it is now.” He
reached behind the irregular hexagonal shield suspended above the
doused coals and took hold of the small mallet stored there. With a
long, measured breath, he struck the metal surface, which tolled a
deep, reverberant sound. “It is done,” Sarek said. He dropped the
mallet to the ground.
About him, the family moved. First, those attending T’Pau lifted her
palanquin and carried her from the ritual site. The others followed
next, all but Spock, who waited until only he and Sarek remained.
Then, as tradition dictated, Spock crossed his hands atop his chest,
and then he too turned and exited the grounds.
In this place where he and Amanda had joined together in matrimony,
where they had brought their son at the age of seven to be bonded for
the pon farr with T’Pring, Sarek stood alone and felt lost. It is the
natural order of things, he told himself. Each life begins, each life
ends.
For all his life, he had believed that his reason would always prove
victorious over his emotions, but right now, his arguments to himself
went for naught. Those emotions that he had for so long mastered would
no longer be denied. Oddly enough, his logic prescribed that he accept
the reality of his situation, which necessarily included the loss of
control over his feelings.
Amanda gone, her katra lost, Sarek thought. He knew that her wishes
had been that, upon her death, her organs be donated to the medical
system on Earth for patients in need, with the rest of her remains
given to a medical school for educational purposes. But effectively
nothing of her body had been left after the crash.
Around Sarek, hot gusts blew, perpetuating the light clink of the
chimes. He stepped down from the platform and crossed toward the
square-arched entryway. The dirt grated beneath his shoes.
Outside the great stone ring, Spock waited. Custom held that, when
possible, the immediate family of the deceased walk together from this
place back to their home, but Sarek suspected that his son would have
waited for him even were that not the case. Since Amanda’s death,
Spock had stayed at the house with him, taking leave from his position
at the Vulcan Science Academy. He had assisted with numerous practical
matters-contending with the guests to Amanda’s party, preparing meals,
rescheduling Sarek’s upcoming ambassadorial agenda-but perhaps more
important, he had provided a calming influence in a time of virtual
madness.
As Sarek strode away from his family’s ancestral land, Spock fell in
beside him. “Father,” he said, “though it is tradition, you need not
walk all the way home.”
“I am aware of that, my son,” Sarek said. “My emotional control has
failed me, not my logic.” They had arrived here for the ceremony via
public transporter from Shi’Kahr, and they each carried recall devices
for the return trip. The rest of the family had arrived and departed
in the same manner.
“It is a long journey,” Spock said. “I am concerned for your health.
You have been under tremendous strain, and with your surgically
repaired heart- “
“We will walk,” Sarek said, continuing along. “It is to honor your
mother, a symbolic passage that avows that we leave her neither
quickly nor easily.”
