Dual-frequency MEMS oscillator — what the 6.1298/6.1679 MHz pair means
The DSC6023CI2A-00AD: That dual-frequency capability lets a single oscillator feed two clock domains on the board — a main MCU core clock and a separate peripheral or USB bus clock, for instance — without a second crystal or a PLL multiplier.
That holds the clock edge jitter tight enough for UART, SPI, and I2C timing budgets; for a 6 MHz serial bus, ±25 ppm is about 150 Hz of drift, well within the receiver's capture range.
Obsolete — sourcing posture for the BOM line
Microchip lists this part as Obsolete.