About 20 gunmen, described by the Kenyan government as "heavily armed bandits" opened fire at the site in the early hours of Tuesday morning after reportedly separating Muslims and non-Muslims.
Several people were beheaded, while others were shot in the back of the head, according to Al Jazeera.
Many of the quarry workers killed are reported to have come from the south of the country where Christians make up 80 percent of the population, while Muslims and ethnic Somalis dominate in the north-eastern regions.
Al-Shabab claimed responsibility for the attack, calling it "another successful operation carried out by the Mujahideen".
The quarry in Mandera is close to where Islamists last month singled out and murdered 28 non-Muslims who were grabbed from a bus.
In a separate attack on Monday night in the town of Wajir, one person died and 12 others were wounded when, according to the Red Cross, gunmen hurled grenades and sprayed a bar with bullets.
"Our team is on the ground undertaking assessments of the attack," the Kenya Red Cross said on Tuesday.
Kenya has suffered a series of attacks since invading Somalia in 2011 to attack al-Shabaab, including last year's attack by al-Shabaab at the Westgate shopping mall in Nairobi, in which at least 67 people were killed in the attack involving four gunmen that lasted four days.
Revd John Itumu, Chair of the Kenya Church Association told Premier's News Hour the Church needs to show some leadership, he said:"There isn't a single leader, a clear leader that can galvanise the Kenyan Christian community to speak in one voice. I think that the denominational differences and the preferenances and their priorities have just taken their toll."
Kenyan forces have since joined an African Union force battling the Islamists.
Revd John Itumu, Kenya Church Association:
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