I've come across multiple scriptures and works of Acharyas which describe a Suryakanta gem, which seems to act like a magnifying glass, using sunlight to produce fire. Here's what this chapter of the Shanti Parva of the Mahabharata says:
Two pieces of wood, rubbed together, produce fire. The stone called Suryakanta, coming in contact with the rays of the Sun, produces fire. Any solid metallic substance, heated in fire, dries up water when coming in contact with it. Similarly, the material body produces the mind and its attributes of perception, memory, imagination, etc.
And here's what this excerpt from Kumarila Bhatta's Tantra Vartika, a Purva Mimamsa work, says:
The word "Nirmanthya" signifying only "the fire produced by friction," and as such having its sole purpose in the setting aside of the employing of such fires as are produced either from electric sparks or by striking, or from the solar gem, etc. - why should it be taken to mean the fire produced on the spot?
And here's what this excerpt from Sridhara's Nyaya Kandali, a Vaisheshika work, says:
As a matter of fact we often find that a single effect has got various kinds of circumstantial accessories for its cause. For instance, Fire is produced out of the rubbing of two sticks as well as from the solar gem.
My question is, what is this Suryakanta gem? Are there any scriptures or works of Acharyas that describe what the Suryakanta gem looks like, where it is found, etc.? Is it like the famous Syamantaka gem, which must be divinely obtained, or is it found on Earth?
Note that I don't want scientific speculation, I just want to know what Hindu scripture and the works of Acharyas have to say.