When completing an entire book of the Torah (ex. Bereishis), it is customary in some communities to recite the words
חזק חזק ונתחזק
which is translated out to "be strong, be strong, and let us be strengthened!"
In the Stone Chumash, the word נתחזק is vocalized as נִתְחַזֵּק, nischazeik. However, it has come to my attention that this may be incorrect, as the word is usually vocalized as נִתְחַזַּק, nischazak, as in Shmuel II 10:12, for example:
חֲזַ֚ק וְנִתְחַזַּק֙ בְּעַד־עַמֵּ֔נוּ וּבְעַ֖ד עָרֵ֣י אֱלֹהֵ֑ינוּ וַֽיהֹוָ֔ה יַעֲשֶֹ֥ה הַטּ֖וֹב בְּעֵינָֽיו
"'...Be strong, and let us strengthen ourselves on behalf of our people, and on behalf of the cities of our God: and [then] may God do what is good in his eyes.'"
Translation from Judaica Press via Chabad.org.
Is the zayin in the word properly vocalized with a patach or with a tzeirei?