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Overview

The test sample is a segment of yellow crystal that Black Mesa scientists discovered in the borderworld, Xen. According to the scientists' announcements prior to Gordon entering the test chamber, this particular sample is the purest ever collected and the administrator went to "some lengths" to obtain it. Once on Xen, the player frequently encounters deposits of the crystal; noteworthy deposits include the three large crystals powering Nihilanth's energy shield.

The test sample, when pushed into the anti-mass spectrometer, causes the resonance cascade that begins the events of the Half-Life series.

Trivia

• In Half-Life 2 Episode Two, Eli Vance told Gordon Freeman that the crystal used as "test sample" was brought by the mysterious G-man.

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