The word is pronounced as written, bear in mind though that in Gaelic we pronounce ch as in loch or Bach, and not as in church. Clach as a word, or element of a word, comes up in Scottish place names. Clackmannan, as in the little county, comes from the Gaelic Clach Mhannain, which means the stone of Manau, Manua being an earlier name for the district. Clach is a feminine noun in Gaelic, meaning that an adjective following the word will often have the first consonant changed in pronunciation.
For example, a big stone will be Clach Mhòr, pronounced Clakh vohr. Many Gaelic-speaking areas are famously stony and there are various words for rocks or stones, which will crop up in place-names. Creig, pronounced creg, and rendered crag in modern English and Scots, usually refers to a cliff or to shore-side rocks sticking out of the water.
Carraig, pronounced Carrik, usually refers to a large expanse of rock. Leac, pronounced lyack, is a large flat stone, and the word is also used for a gravestone in colloquial Gaelic. Although the Callanish Stones in Lewis, are often referred to as Clachan Chalanais, the correct term (and the one found on signs) is actually Tursachan Chalanais – pronounced Toor-sakh-khan Khalanish.
Over the years, there have been various attempts to explain the meaning of Tursa in this context. Theories ranged from theorising that since the stone circle was a solemn place it must be related to tùrsach, meaning sad. Others attempted to link it to the word turas, meaning journey, because pilgrims might travel there. Scholars believe it is related to the Old Norse word Tursa, which meant giant, because the stones, especially the central ones, do tower over people. The current Gaelic name is much more recent than the stones themselves.