Post a pic of this lace rock. There are natural and artificial types of "lace rock". Lace agates are simple compressed silicates that are inert in aquaria. Another lace rock is tufa which is a compressed calcium carbonate which will yield an increased pH. The rate and level depends on the level of compression of the rock. Man-made lace rock is a form of aragocrete and, if properly made, will only slightly increase pH. However, factory seconds and improperly made lots of lace rock have been found to jump pH to over 9.0.
As stated, soaking and testing is preferred to remove doubts.