What feldspar is greenish blue with gridlike white streaks, resembling turquoise?

The correct identification of feldspar that is greenish blue with gridlike white streaks resembling turquoise would be Amazonite. Amazonite is known for its distinctive color, which can range from a soft green to a brighter bluish-green, often displaying white streaks or veins due to the presence of other minerals. These characteristics result in a striking appearance that indeed can be reminiscent of turquoise.

While moonstone primarily features a unique optical phenomenon called adularescence and may exhibit bluish or golden sheen, it does not typically display the gridlike streaks or the specific color associated with the correct answer. Labradorite often showcases a play of color known as labradorescence, but it does not resemble turquoise in terms of color and markings. The term "medium green" lacks specificity and does not refer to a distinct type of feldspar associated with these characteristics.

Thus, Amazonite accurately fits the description of the greenish blue feldspar with distinctive markings that resemble turquoise.