This is fused quartz.
This is College Physics Answers with Shaun Dychko. An unknown material is submerged in water and we have a beam of light with an angle of incidence 45 degrees. So, <i>theta one</i> is 45. And, we can also measure the angle of refraction here, which is 40.3 degrees. And, we know that since this material is immersed in water, the initial index of refraction is 1.33. And, Snell's law says that index of refraction of the first material times sine <i>theta one</i> equals index of refraction of the second material, which we don't know, multiplied by sine <i>theta two</i>, which we do know. So, we'll solve this for <i>N two</i> by dividing both sides by sine <i>theta two</i>. So, <i>N two</i> is <i>N one</i> sine <i>theta one</i> over sine <i>theta two</i>. So, that's 1.33 index of refraction of water times sine of 45 degrees incidence angle divided by sine of 40.3 degrees angle of refraction, giving us 1.45. And, looking in table 25.1, this appears to be fused quartz.