Apple Inc.’s stock market value peaked on Tuesday for a second day above a $3 trillion, but the iPhone maker’s shares again failed hold that gain by the session’s end. Apple shares ended down 1.3 percent at $179.70, leaving its market capitalization at $2.95 trillion. On Monday, Apple’s stock market value rose briefly above $3 trillion for the first time ever, and it repeated that again on Tuesday before losing ground. The world’s most valuable company has yet to end a session at that level. Apple accounts for nearly 7 percent of S&P 500 index’s value, according to Refinitiv data, the highest for a single stock in the index at a time when the benchmark is perched at a peak. Surging demand for iPhones, MacBooks, and iPads during the pandemic helped push the Cupertino, California company’s market capitalization past $2 trillion in August 2020. “Apple has been one of the …