I heard that the US forces in the pacific used landing craft with tracks on to clear sandbars and coral

You heard correctly. Amtraks (LVT, Landing Vehicle Tracked, or amphitrack, or amtrac) were indeed used in the Pacific Theater. They were quite good at getting over the sandbars and coral reefs of the various Pacific islands that were assaulted during the war. Their ability to get over coral reefs was especially prized, as other landing options (LCVP's, DUKW's, boats, etc) were unable to simply crawl over the reefs like the Amtraks could. The result was that some times troops would have to disembark on the reef and attempt to wade in to shore. This was a costly approach, especially at Tarawa.

Early versions were open-topped, but that became a liability in combat landings. In later models a rear ramp was added which allowed troops to disembark in the relative safety of having the bulk of the machine between themselves and the enemy. Later models also gained more armor to rectify the vulnerabilities of the first models. Some models were also given small tank turrets or mortars to work as fire support.

As to their lack of use in Torch, Anzio, or Normandy you are correct. However, these beaches were able to be approached with the shallow-draft LCVP (Higgins boat). There were never enough LVT's to go around, so keeping them largely in the Pacific where they were needed to get across those reefs was a sound policy. They were used for river crossings (the Rhine, the Po) in Europe though, as well as the rather nasty Battle of the Scheldt when Canadians and British soldiers used them to make the port of Antwerp available to the Allies. Still, they are rightly associated with their service in the Pacific, as their usage in Europe was sporadic and highly localized. If you were to see a picture like this you would likely think "Pacific theater"--and you would be right more times than not.